A Monograph on the Sub-class Cirripedia Part 19

Having dissected the six specimens with the utmost care, and having scrupulously examined the ovaria in other Cirripedes during their early stages of development, even before the exuviation of the larval locomotive organs, and in specimens of smaller size than the male Ibla, I am prepared to a.s.sert that there are no ovaria, and that these little creatures are exclusively males. It should be borne in mind, that in some of the specimens there were perfect spermatozoa in the vesiculae seminales (as likewise in some of the males of _I. quadrivalvis_), and, therefore, if these individuals had been hermaphrodites, their ova would have been, at this period, well developed, and ready for impregnation: in this state it is almost impossible that they could have been overlooked. Moreover, it is probable that such ova would not have been very small, for the larvae whence the parasitic males are derived, attain (as might have been inferred from the known dimensions of their prehensile antennae, and as we shall show actually is the case in _I.

quadrivalvis_,) the size common amongst ordinary Cirripedia.

_Concluding Remarks._--That these animals are true Cirripedes, though having so different an external appearance from others of the cla.s.s, admits of not the least doubt. The prehensile antennae, enveloped in cement and including the two cement-ducts, would have been amply sufficient, without other parts--for instance, the mouth, by itself perfectly characteristic with each organ, together with the whole alimentary ca.n.a.l, constructed on the normal plan,--to have proved that they were Cirripedia. Under the head of the closely-allied _Ibla quadrivalvis_, we shall, moreover, see that the males are developed from larvae, having every point of structure--the peculiar quasi-bivalve sh.e.l.l, the two compound eyes, the six natatory legs, &c.,--characteristic of the Order. But in some respects, the males are in an embryonic condition, though unquestionably mature, as shown by the spermatozoa;--thus, in the thorax and mouth opening throughout their whole width into the cavity of the peduncle, that is, h.o.m.ologically into the anterior part of the head, and in the viscera being there lodged instead of in the thorax and prosoma, there is a manifest resemblance to the larva in its last stage of development: the absence of a probosciformed p.e.n.i.s, the spineless peduncle, the food being obtained without the aid of cirri, and the length of the r.e.c.t.u.m, are likewise embryonic characters. Not only are these males, as just remarked, Cirripedia; but they manifestly belong to the Pedunculated Family. If a specimen had been brought to me to cla.s.s, without relation to its s.e.xual characters, I should have placed it, without any hesitation, next to the genus Ibla; if the mouth alone had been brought, I should a.s.suredly have placed it actually in the genus Ibla: for let it be observed how nearly all the parts resemble those of _Ibla c.u.mingii_, excepting only in size and in being less hairy. The trophi are arranged in the same peculiar position as in the female; the labrum is largely bullate, without teeth on the crest; the palpi, though relatively smaller, are of the same shape; so are the mandibles; the maxillae are more rounded and less prominent, but have the same exact size relatively to the mandibles; the outer maxillae have the same, quite peculiar pointed outline, and the olfactory orifices are tubular, and hold the same unusual position. It is most rare to find so close a resemblance in the parts of the mouth, except in very closely allied genera, and often species of the same natural genus differ more. Again, in the long oesophagus and constricted stomach there is a resemblance to Ibla. In the male of _Ibla quadrivalvis_, the caudal appendages are multi-articulate; now, this is a character confined to four genera, namely, Ibla, Alepas, Pollicipes, and Lithotrya. I may add, that large tubular olfactory orifices are confined to the same genera, together with Scalpellum. Lastly, it particularly deserves notice, that the prehensile antennae, in having a hoof-like and pointed disc, with a single spine on the heel, much more closely resemble these organs in Scalpellum, certainly the nearest ally of Ibla, than in any other genus; they differ from the antennae in Scalpellum, only in the ultimate segment not having a notch on one side.

These organs, unfortunately for the sake of comparison, were not found in the female and ordinary form of Ibla. The full importance of the above generic resemblance in the antennae, will hereafter be more clearly seen, when their cla.s.sificatory value is shown in the final discussion on the s.e.xual relations of Ibla and Scalpellum.

Here, then, we have a pedunculated Cirripede _very much_ nearer in all its essential characters to Ibla than to any other genus, and exclusively of the male s.e.x; and this Cirripede in six specimens, from two distant localities, adhered to an Ibla exclusively of the female s.e.x. May we not, then, safely conclude that these parasites are the males of the _Ibla c.u.mingii_? Considering that, in the same cla.s.s with the Cirripedia, there is a whole family of crustaceans, the Lerneidae, in which the males, compared with the females to which they cling, differ as much in appearance as in Ibla, and are even relatively smaller, I should not have added another remark, had there not been under the head of the following species, and of the next genus Scalpellum, a cla.s.s of allied facts to be advanced, which in some respects support the view here taken, but in others are so remarkable and so hard to be believed, that I will call attention to the alternative, if the above view be rejected. The ordinary _Ibla c.u.mingii_ must have a male, for that it is not an hermaphrodite can hardly be questioned, seeing how easy it always is to detect the male organs of generation; and we must consequently believe in the visits of a locomotive male, though the existence of a locomotive Cirripede is improbable in the highest degree. Again, as the little animal, considered by me to be the male of _I. c.u.mingii_, is exclusively a male, (for there were no traces of ova or ovaria, though the spermatozoa were perfect,) we must believe in a locomotive Cirripede of the opposite s.e.x, though the existence in any cla.s.s of a female visiting a fixed male is unknown:[48] in short, we should have hypothetically to make two locomotive Cirripedes, which, in all probability, would differ as much from their fixed opposite s.e.xes, as does the Cirripede, considered by me to be the male of _I. c.u.mingii_, from the ordinary form. This being the case, I conclude that the evidence is amply sufficient to prove that the little parasitic Cirripede here described, is the male of _Ibla c.u.mingii_.

[48] It deserves notice, that in the cla.s.s Crustacea, both in the Lerneidae and in the Cirripedia, the males more closely resemble the larvae, than do the females; whereas amongst insects, as in the case of the glow-worm in Coleoptera, and of certain nocturnal Lepidoptera, it is the female which retains an embryonic character, being worm-like or caterpillar-like, without wings.

But in all these cases, the male is more locomotive than the female.

If we look for a.n.a.logies to the facts here given, we shall find them in the Lerneidae already alluded to, but in these the males are not permanently attached to the females, only cling, I believe, to them voluntarily. The extraordinary case of the Hectocotyle, originally described as a worm parasitic on certain Cephalopoda, but now shown by Kolliker to be the male of the species to which it is attached, is perhaps more strictly parallel. So again in the entozoic worm, the _Heteroura androphora_ the s.e.xes cohere, but are essentially distinct: "this singular species, however," according to Professor Owen,[49]

"offers the transitional grade to that still more extraordinary Entozoon, the _Syngamus trachealis_, in which the male is organically blended by its caudal extremity with the female, immediately anterior to the slit-shaped aperture of the v.u.l.v.a. By this union a kind of hermaphroditism is produced; but the male apparatus is furnished with its own peculiar nutrient system; and an individual animal is const.i.tuted distinct in every respect, save in its terminal confluence with the body of the female. This condition of animal life, which was conceived by Hunter as within the circle of physiological possibilities, has. .h.i.therto been exemplified only in the single species of Entozoon, the discovery of the true nature of which, is due to the sagacity and patient research of Dr. C. Th. Von Siebold." In Ibla, the males and females are not organically united, but only permanently and immovably attached to each other. We have in this genus the additional singularity of occasionally two males parasitic on one female.

[49] Cyclopaedia of Anatomy and Physiology, p. 142.

I have used the term parasitic, which perhaps ought strictly to be confined to cases where one creature derives its nutriment from another, inasmuch as the male is invariably and permanently attached to and imbedded in the female,--from its being protected by her capitulum, so that its own capitulum is not developed--and from its feeding on minute animals infesting her sack. The male Ibla must seize its prey, guided probably by its well-developed olfactory organs, through the movement of its long, flexible body, furnished with muscles, and with the mouth seated on the summit. We have already seen one instance of a Cirripede, the Anelasma, obtaining its food without the aid of cirri, by means of its probosciformed, flexible mouth. The eye can serve only to announce to the male when the female opens her valves, allowing occasionally some minute prey to enter. In ordinary Cirripedes the p.e.n.i.s is long, articulated, and capable of varied movements, I presume for the purpose of impregnating each separate ovum: the male Ibla has no such organ; and no doubt the whole body, furnished like the p.e.n.i.s with longitudinal and transverse muscles, serves the same purpose! I may remark, that it seems surprising that so small a male should secrete sufficient s.e.m.e.n to impregnate the ova of the female, but the ova are not nearly so numerous in Ibla as in most genera of Cirripedes; and the smallness of the males in some parasitic Crustacea has already been alluded to. The male must always be younger than the female, for the latter must first grow large enough for the larva of the male to crawl into her sack. Whether the male lives as long as the female I know not, but he certainly lives for a considerable period and increases in size, as shown by the depth to which the end of the peduncle is imbedded. Moreover we shall see, under the next species, that the male is metamorphosed from a larva, not one sixth of its own size.

In the male Ibla, abortion has been carried to an extraordinary and, I should think, almost unparalleled extent. Of the twenty-one segments believed to be normally present in every Crustacean, or of the seventeen known to be present in Cirripedes, the three anterior segments are here well developed, forming the peduncle: the mouth consists as usual of three small segments: the succeeding eight segments are represented by the rudimentary and functionless thorax, supporting only two pair of distorted, rudimentary and functionless cirri: the seven segments of the abdomen have disappeared, with the exception of the excessively minute caudal appendages; so that, of the twenty-one normal segments, fifteen are more or less aborted. The state of the cirri is curious, and may be compared to that of the anthers in a semi-double flower; for they are not simply rudimentary in size and function, but they are monstrous, and generally do not even correspond on opposite sides of the same individual. As males in other cla.s.ses of the animal kingdom often retain some female characters, so here (though the case is not strictly a.n.a.logous[50]) the male possesses the cementing apparatus, which h.o.m.ologically is part of an ovarian tube modified.

[50] Certain plants offer a closer, though not perfect, a.n.a.logy.

Thus, in the florets of some compositous flowers, the pistil, besides its proper female functional end, serves to brush the pollen off the anthers; while, in the florets of some other compositae (see the account of Silphium in 'Ch. K. Sprengel Das entdeckte Geheimniss der Natur'), the pistil is functionless for its proper end, the flower being exclusively male, but its style is developed, and still serves as a brush. So in the male Ibla, part of the ovaria, in a modified condition, is still present, and serves as a cementing apparatus.

The individuals in every other genus (with the exception of Scalpellum), in the several families, in the three Orders of Cirripedia, are hermaphrodite or bis.e.xual. Why, then, is Ibla unis.e.xual; yet, becoming, in the most paradoxical manner, from its earliest youth, essentially bis.e.xual? Would food have been deficient, and was the seizure of infusoria by another and differently constructed individual, necessary for the support of the male and female organs? The orifice of the sack of the female is unusually narrow; would the presence of testes and vesiculae seminales have rendered her thorax and prosoma inconveniently thick? Seeing the a.n.a.logous facts in the six, differently-constructed species of the allied genus Scalpellum, I infer there must be some profounder and more mysterious final cause.

2. IBLA QUADRIVALVIS. Pl. IV, fig. 9.

ANATIFA QUADRIVALVIS. _Cuvier._ Mem. pour servir ... Mollusq.

1817, Art. Anatifa, Plate, figs. 15, 16.

IBLA CUVIERIANA. _J. E. Gray._ Annals of Philosophy, vol. x, New Series, Aug. 1825.

---- _J. E. Gray._ Spicilegia. Zoolog. Tab. iii, fig. 10.

TETRALASMIS HIRSUTUS. _Cuvier._ Regne Animal, vol. iii, 1830.

ANATIFA HIRSUTA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.

xciii, figae. 7-10, 1834.

_I. (Herm.), valvis et pedunculi spinis sub-flavis: basali tergorum angulo, introrsum spectanti, hebete, quia margo carinalis inferior longius quam margo scutalis prominet._

_Hermaph._--Valves and spines on the peduncle yellowish: basal angle of the terga, viewed internally, blunt, owing to the lower carinal margin being more protuberant than the scutal margin.

Caudal appendages four times as long as the pedicels of the sixth cirrus: rami of the first cirrus unequal in length by about six segments.

_Complemental Male_, with a notched crest on the dorsal surface, forming a rudiment of a capitulum: maxillae well furnished with spines.

Kangaroo Island, South Australia (Mus. Brit., given by Cuvier to Leach); Adelaide, South Australia (Mus. Stutchbury); King George's Sound, Voyage of Astrolabe; New South Wales, attached to a ma.s.s of the Galeolaria dec.u.mbens, (Mus. Hanc.o.c.k).

HERMAPHRODITE.

All the external parts so closely resemble those of _I. c.u.mingii_, that it would be superfluous to describe more than the few points of difference. The h.o.r.n.y substance of both scuta and terga is uniformly yellow; though in dryed specimens, from the underlying corium being seen through the valves, these generally have a tinge of blue.

The _Scuta_, viewed internally, are less elongated transversely; they have their basal margins slightly more hollowed out, and the fold on the upper free and horn-like portion rather deeper.

The _Terga_, viewed internally, have the apex of the growing or corium-covered surface higher relatively to the scuta than in _I.

c.u.mingii_; and the basal angle is much broader, owing to the lower carinal margin being much more protuberant than the scutal margin. The spines on the peduncle are all yellowish-brown, and are rather longer than in _I. c.u.mingii_. I observed in three or four specimens, that the lowest part of the peduncle had become _internally_ filled up with the usual, brown, transparent, laminated cement, cone within cone, so that this lower part was rendered rigid and stick-like; this latter effect, I apprehend, is the object gained by the formation of cement within the peduncle, of which I have not observed any other instance. The entire length of the largest specimen was one inch; some other specimens were only half this size.

The thorax and prosoma are of the same shape as in _I. c.u.mingii_, and in the largest specimen, about one tenth of an inch square; the prosoma, as in that species, is hairy. In the _Mouth_, all the parts are closely similar to those of _I. c.u.mingii_, but one third larger; the crest of the labrum is a little roughened with minute points: the palpi are squarer and blunter at their extremities: the mandibles have their second and third teeth nearly equal in size to the first, and they do not appear pectinated: the maxillae have their spinose edge very nearly straight: the outer maxillae are pointed. The olfactory orifices are similarly situated, and of similar shape; they are dark coloured.

_Cirri._--These also are similar to those of _I. c.u.mingii_; the segments, however, of the three posterior cirri have each four pair of spines, placed very close together in a transverse direction. First cirrus has its two rami unequal in length by about six segments. The anterior rami of the second and third cirri are thicker, and more thickly clothed with spines, than the posterior rami, to perhaps a greater degree than in _I. c.u.mingii_. In the posterior cirri, the upper segments of the pedicels are nearly as long as the lower segments.

_Caudal Appendages_, four times as long as the pedicel of the sixth cirrus, and three fourths of the length of the rami of this same cirrus: segments thirty-two in number, and therefore as many as those forming the sixth cirrus: the upper segments are much thinner and longer than the basal segments; each furnished with a circle of short bristles; whole appendage excessively thin and tapering: the two closely approximate.

_Colour._--From some well-preserved dryed specimens in Mr. Stutchbury's possession, it appears that the sack, cirri and trophi, were dark blue, as in _I. c.u.mingii_; after being long kept in spirits, these parts become brown.

_Generative System._--The p.e.n.i.s (Pl. IV, fig. 9 _a_) is very singular in structure; it is of the ordinary length, but of small diameter; it tapers but little; it consists of a moveable articulated, and a fixed unarticulated portion; this latter is smooth, much flattened, not divided into segments, and projects straight out under the caudal appendages; it is about one third of the length of the entire p.e.n.i.s; it corresponds with a part present in all Cirripedes, but here surprisingly elongated. The articulated portion consists of separate segments, twenty in number, quite as distinct as those of the cirri; each one is oblong, being longer by about a third part than broad; each has a few short bristles round its upper margin; the terminal segment has a circular brush of bristles. The vesiculae seminales are easily seen, though they are narrow; they are slightly tortuous; they enter the prosoma, and lie on each side of the stomach; their outer case has a ringed structure, but is not fibrous; the contents in the best specimen consisted of a ma.s.s of spermatozoa, which I saw with perfect distinctness. The testes are unusually large and egg-shaped.

_Ova_, spherical, 5/400ths of an inch in diameter, united as usual into two ovigerous lamellae. The ovigerous fraena are extraordinarily small, and might be very easily overlooked; their length, in a full-sized specimen, was only 7/400ths of an inch, and they projected only 2/400ths from the inner surface of the sack. The glands on their margin, to which the lamellae adhere, are pointed oval, with an extremely short footstalk, and that rather thick; the entire length of gland and footstalk, being only 2/3000ths of an inch. The larvae, in their first stage of development, offer the usual characters, and closely resemble those of Scalpellum; the probosciformed mouth, however, is remarkably prominent, and the limbs unusually thick.

_Affinities._--This species most closely resembles _I. c.u.mingii_, and cannot be distinguished externally, except by the absence of the blue colour on the marginal and interior portions of the valves; and this can hardly be ascertained without separating and cleaning them, owing to the blueness of the underlying corium. Internally some slight differences may be perceived in the form of the valves. Considering these so slight differences, it is highly remarkable that this species should be hermaphrodite, whilst _I. c.u.mingii_ is unis.e.xual. There is a greater, though still slight, difference in the included animal's body; the palpi in _I. quadrivalvis_ are blunter, the mandibles smoother, the olfactory orifices darker-coloured; the rami of the first cirrus more unequal, the spines more numerous on the segments of the posterior cirri, and lastly and most conspicuously, the caudal appendages are very much longer relatively to the length of the sixth cirrus, than in _Ibla c.u.mingii_.

COMPLEMENTAL MALE.

I have examined one specimen of the hermaphrodite _I. quadrivalvis_, preserved in spirits from Kangaroo Island, and one dry from Adelaide, both places in South Australia, and four from an unknown locality, purchased from Mr. Sowerby; and within five out of these six specimens, males were attached. In one of them, two males of different ages were included, one adhering to the peduncle of the other: in _I. c.u.mingii_, also, it may be remembered, there was a case of two males parasitic on one female. I may add that I opened another quite young specimen, from Adelaide, not counted with the above, and it was without a male. The males in the five specimens were attached low down, at the rostral end, almost in a horizontal position, stretching across the bottom of the sack; one of them, however, was placed considerably on one side. One individual which I measured, was 16/100ths of an inch in length, and 5/100ths in width in the widest part, namely, about half down the peduncle. I may state, for the sake of comparison, that the hermaphrodite to which this individual was attached, was, including the peduncle and capitulum, one inch in length, that is, six times as long as the male, and one fifth of an inch in width, that is, four times as wide. The above measurements show that the male of this species is rather more than twice as large as that of _I. c.u.mingii_. In consequence of this greater size, I dissected, with the utmost care, the one specimen which was excellently preserved in spirits, and found every part, with a few exceptions, so exactly the same as in the male of _I.

c.u.mingii_, only larger and more conspicuous, that it will be sufficient to indicate the few points of difference.

The most conspicuous difference is, that the oblique fold separating the thorax and peduncle is more plainly developed, projecting at the point corresponding to _h_ in fig. 1, Pl. V, 8/1000ths of an inch; in the middle the fold is notched; it can be traced more easily than in _I.

c.u.mingii_, running beneath and parallel to the basal edge of the mouth, to the ventral margin of the body. In the mouth there is hardly any difference; the maxillae, however, have two notches even plainer than in the hermaphrodite _I. quadrivalvis_, or than in the male _I. c.u.mingii_, but the depth of such notches is always a variable character; there are also more spines on the edge in the male of the present species, than in _I. c.u.mingii_. Both mandibles and maxillae in the male _I. quadrivalvis_, are larger than in the male _I. c.u.mingii_, to a greater degree than the larger proportional size of the body in the former will account for; and this, likewise, is the case with these same organs in the hermaphrodite _I. quadrivalvis_ compared with the female _I. c.u.mingii_. The tubular olfactory orifices are situated in the same peculiar position as in the hermaphrodite, and as in both s.e.xes of _I. c.u.mingii_: they are 1/500th of an inch in diameter, and about as thick as one of the lower segments in the rami of the sixth cirrus.

The thorax, as in the male of _I. c.u.mingii_, is quite rudimentary, and serves as a mere flap to protect the mouth. In the three specimens carefully examined, the posterior cirri had each only one ramus, whilst the anterior cirri generally had two: in one specimen, one of the rami in the anterior cirrus was formed of five segments, and the other ramus of three segments, both rami being supported on a uni-articulated pedicel; but on the opposite side of the same individual, the anterior cirrus was represented by a mere k.n.o.b. The longer ramus of the anterior cirrus, in the best-developed individual, barely exceeded in length the mandibles measured along the line of the teeth! In one specimen between the bases of the posterior cirri, there were two perfectly distinct caudal appendages; these, like the cirri, are in a quite rudimentary condition; one was 5/1000ths of an inch in length, and consisted of three segments, the upper edges of which had short spines; the other was shorter, uni-articulated, but spinose. In a second specimen, these appendages were quite aborted. Close under them, on the inside or towards the mouth, (that is, in the normal position,) there was a rudimentary but quite distinct p.e.n.i.s, with the apex projecting freely, and with the sides distinguishable from the ventral surface of the thorax, for the length of 1/1000th of an inch: the corium lining this little p.e.n.i.s made the terminal orifice plainly visible. The vesiculae seminales lie in the usual position, and are conspicuous; they are slightly tortuous, with their ends blunt: in the specimen so well preserved in spirits, they were filled with a ma.s.s of spermatozoa, perfectly distinct; and the whole cavity of the body was lined with globular and pear-shaped testes. a.s.suredly there was no vestige of ovarian tubes. From the greater size and excellent preservation of this specimen, which rendered the examination of the generative system so easy, I was able to examine the contents of the stomach, in which I found the delicate epithelial coat, separated as usual, and containing cellular matter, on which the animal had preyed, but the nature of which I was unable to make out. The a.n.u.s was much plainer than in the male of _I. c.u.mingii_. I saw the eye distinctly. I could not distinguish the orifices of the acoustic (?) sacks; and I think I should have seen them, if they had existed.

_Prehensile Antennae._--I examined these in the larvae presently to be mentioned, and therefore they were in better condition than in the mature animal when cemented. Their total length, measured along the outside, from the basal articulation to the end of the disc, is 32/6000ths or 33/6000ths of an inch--that is, one third longer than in _I. c.u.mingii_; whilst the hoof-like disc itself is 8/6000ths, or only 1/6000th of an inch longer than this same part in _I. c.u.mingii_: the apex of the disc is downy, or bears some excessively minute spines. The ultimate segment has its end irregularly rounded, with the spines obscurely divided into two groups, the outer group consisting of two or three longer and thinner spines, and the inner group of, as I believe, five rather shorter spines: the longer spines equal in length the whole ultimate segment. I could not perceive that they were plumose, as in many other genera. A single, rather thicker and long spine, pointing backwards, is attached to the under side of the disc, nearly opposite to the point where the ultimate segment is articulated on the upper convex surface. Another single, curved spine is attached on the outer side of the basal segment, near its distal end.

_Development of the Male._--In the specimen before alluded to, which included two males, one of these was only the 30/1000ths of an inch in length, and therefore between one fifth and one sixth of the size of the mature male. It had, probably, undergone only one exuviation since its metamorphosis, for the larva is nearly as long, namely, 25/1000ths of an inch. In this young male, the mouth formed one third of the entire length: it was attached, not as in every other case to the sack of the hermaphrodite, but low down to the peduncle of the other male.

In the sack with these two males, there were certainly four, I believe five, larvae, which in every main point of structure resembled the larvae of other pedunculated Cirripedes. From the peculiar form of their prehensile antennae, differing in no respect, except in the proportional lengths of the segments, from the same organ in the male _I. c.u.mingii_, I can feel no doubt that these were the larvae of the male _I.

quadrivalvis_;--for a moment's reflection will show how excessively improbable it is, that several larvae of some other Cirripede, and that a Cirripede intimately allied to the parasitic male Ibla, should have forced themselves, without any apparent object, into the sack of the hermaphrodite Ibla. The larvae, though not yet attached, were on the point of attachment, so that the single eye of the mature animal could be distinctly seen, lying near to the two great compound eyes of the larva. We have also just seen, that one male quite recently here had undergone its metamorphosis. The larvae are 25/1000ths of an inch in length, and rather more than 10/1000ths in width in the widest part: they are boat-shaped, the dorsal edge forming the keel of the boat; the anterior end is only a little blunter than the posterior end; the quasi-bivalve carapace is smooth. All the essential points of structure in the larvae of other Cirripedes at this stage, could be distinctly here seen,--such as the two compound eyes, with the apodemes to which they are attached, and the two oblong sternal plates whence the apodemes spring,--the adductor muscle,--the six natatory legs, with long plumose spines,--the abdomen, with its three small segments and the caudal appendages,--the prehensile antennae already described,--and, lastly, the two little (auditory?) sacks at the antero-sternal edges of the carapace, but not so near the anterior extremity as in Lepas. The four or five larvae, after having undergone in the open sea the several preparatory metamorphoses common to the cla.s.s, must have voluntarily entered the sack of the hermaphrodite: ultimately would they, on finding two males already attached there, have retired, and sought another individual less well provided; or would they all have remained, and so formed a polyandrous establishment, such as we shall presently see occurs sometimes in Scalpellum? This must remain quite uncertain.

In this same hermaphrodite specimen of _I. quadrivalvis_, the two ovigerous lamellae contained some hundreds of larvae in the first stage of development, which were liberated from their enveloping membranes by a touch of a needle: they were about the 16/1000ths of an inch in length, and presented all the usual characters of larvae at this period. What a truly wonderful a.s.semblage of beings of the same species, but how marvellously unlike in appearance, did this individual hermaphrodite present! We have the numerous, almost globular larvae, with lateral horns to their carapaces, with their three pair of legs, single eye, probosciformed mouth and long tail:--we have the somewhat larger larvae in the last stage of development, much compressed, boat-formed, with their two great compound eyes, curious prehensile antennae, closed rudimentary mouth and six natatory legs so different from those in the first stage:--we have the two attached males, with their bodies reduced almost to a mouth placed on the summit of a peduncle, with a minute, apparently single eye shining through the integuments, without any carapace or capitulum, and with the thorax as well as the legs or cirri rudimentary and functionless:--lastly, we have the hermaphrodite, with all its complicated organisation, its thorax supporting six pairs of multi-articulated two-armed cirri, and its well-developed capitulum furnished with h.o.r.n.y valves, surrounding this wonderful a.s.semblage of beings. Unquestionably, without a rigid examination, these four forms would have been ranked in different families, if not orders, of the articulated kingdom.

_Concluding Remarks._--If the creature which I have considered as the male of _Ibla c.u.mingii_ be really so, and the evidence formerly given seems to me amply conclusive, then the animal just described, from its close affinity in every point of structure with the former, a.s.suredly is the male of _Ibla quadrivalvis_. But feeling strongly how improbable it is, that an additional or complemental male should be a.s.sociated with an hermaphrodite, I will make a few remarks on the only possible hypothesis, if my view be rejected,--namely, that the two parasites considered by me to be exclusively males, are not so, but are independent hermaphrodite Cirripedes, the female organs and ova (which, if present, would have been nearly mature, judging from the presence of spermatozoa in both species) having been overlooked by me in every specimen: and again, that in the animal described as the female _I.

c.u.mingii_, I have, though minutely dissecting several specimens, and finding far smaller parts, such as the organs of sense and nervous system, entirely overlooked all the conspicuous male organs, though when I came to _I. quadrivalvis_, and naturally expected to find it likewise exclusively female, a single glance showed me the great probosciformed p.e.n.i.s, and by the simplest dissection the vesiculae seminales and testes were exhibited. Such an oversight is scarcely credible; but even if a.s.sumed, we have to believe in the extraordinary circ.u.mstance of the two parasites being species of an independent genus, not only the very next in alliance to the animals to which they are attached, but in certain most important points, namely, the organs of the mouth, actually deserving a place in the very same genus. Moreover, the two parasites differ from each other, not only in about the same slight degree, but in a corresponding manner, as do the two Iblas to which they are attached; thus the mouths of _Ibla quadrivalvis_ and _I. c.u.mingii_ are closely similar, (the difference being barely of specific value,) so are the mouths of the two parasites; but the parts are larger in the hermaphrodite _I. quadrivalvis_, than in _I. c.u.mingii_, so are they in the parasites. Again, the most conspicuous character in _I.

quadrivalvis_, is the number of segments in the caudal appendages, far exceeding those in the other species of Ibla, as well as of every other pedunculated Cirripede, and the parasite of this species has articulated spinose appendages, far larger than the barely visible, non-articulated pair in _I. c.u.mingii_.

Considering the whole case, there seems no room to doubt the justness of the conclusion arrived at, under the former as well as under the present species, namely, that these little parasites are the males of the two species of Ibla to which they are attached;--wonderful though the fact be, that in one case, the male should pair with an hermaphrodite already provided with efficient male organs. It is to bring this fact prominently forward, that I have called such males, Complemental Males; as they seem to form the complement to the male organs in the hermaphrodite. We look in vain for any, as yet known, a.n.a.logous facts in the animal kingdom. In the genus Scalpellum, however, next in alliance to Ibla, in which, consequently, if anywhere, we might expect to find such facts, they occur; and until these are fully considered, I hope the conclusions here arrived at, will not be summarily rejected. Although the existence of Hermaphrodites and Males within the limits of the same species, is a new fact amongst animals, it is far from rare in the Vegetable Kingdom: the male flowers, moreover, are sometimes in a rudimentary condition compared to the hermaphrodite flowers, exactly in the same manner as are the male Iblas. If the final cause of the existence of these Complemental Males be asked, no certain answer can be given; the vesiculae seminales in the hermaphrodite of _Ibla quadrivalvis_, appeared to be of small diameter; but on the other hand, the ova to be impregnated are fewer than in most Cirripedes. No explanation, as we have seen, can be given of the much simpler case of the mere separation of the s.e.xes in _Ibla c.u.mingii_: nor can any explanation, I believe, be given of the much more varied arrangement of the parts of fructification in plants of the Linnean cla.s.s, Polygamia.