A Guide for the Study of Animals Part 34

c. _Stomach_, white and muscular, beginning with a very short esophagus and ending as a blind sac. If it is much distended, open it to see what the fish may have eaten.

d. _Small intestine_, thin-walled, tubular, and somewhat coiled.

e. _Large intestine_, a short, thin-walled expansion at the posterior end of the small intestine; usually less than half an inch long.

f. _Cca_, from two to several small pouches attached where the small intestine leaves the stomach.

4. _Spleen_, a reddish brown _globule_ between the folds of the intestine.

5. _Swim bladder_, an elongated chamber lying against the backbone, part.i.tioned off from the cavity below by a delicate membrane.

6. _Peritoneum_, the delicate, silvery membrane which lines the abdominal cavity and enfolds the viscera. Note its spots of pigment.

7. _Pericardial chamber_, the chamber around the heart; see -- 1 above.

8. _Heart._ As the fish is placed belly upward in the pan the _ventricle_ faces you, pink, conical, and muscular. Posterior to it, on the dorsal side, is the _auricle_, a membranous sac.

9. _Ventral aorta_, arising on the anterior surface of the ventricle as a white muscular "cord" (really a tube) which is enlarged close to the heart into a bulb, the _arterial bulb_. You should follow up this aorta until you see it divide right and left to send its branches outward into the gills, the branches being called _gill arteries_.

_Questions._

1. The fish frequently swallows its food alive. Why should the stomach be muscular? Why is it better that the intestine does not leave the stomach at the end opposite the esophagus?

2. Of what use can the cca be? What structure of the human intestine do you recall that is at all like them in form or use?

3. How many times the length of the body is the length of the alimentary ca.n.a.l? Does this indicate that the fish is compelled to eat a great deal of poor food or that its food is highly nutritious, so that little need be taken?

4. Near which end of the fish's body is the heart? Is this the usual or the unusual condition among animals you know about? What advantages can you think of in this arrangement?

5. What advantages are there in having the heart in a chamber separated from the other vital organs?

6. Of how many chambers does the heart consist? Why should at least one of them be muscular?

7. How many times does the blood pa.s.s through the heart in making a complete circuit of the body? Would you call this a single or a double circulation?

8. Does the heart force the blood onward or does it draw blood into itself, _i.e._ is the heart a force pump or is it a suction pump?

9. How is circulation made complete? If the heart is a force pump, is its power sufficient to drive blood through artery, capillary, vein, and into auricle, if the capillaries can stand the pressure, or is another action concerned? If it is a suction pump, why does the blood leave the heart?

_Suggested drawings._

a. The body cavity, with viscera undisturbed.

b. The alimentary ca.n.a.l extended.

c. The anterior end of the fish with the sinus held open, to show the general situation of the parts.

d. The heart in its chamber, with the outgoing vessels as far as dissected. Use arrows to show direction of circulation.

e. A copy of some good diagram or chart which ill.u.s.trates the heart of the fish with the connecting veins and arteries.

Fishes: A General Review and Library Exercise

1. Food and the feeding habits of young and of adult fishes.

2. The diet and habits of cod; lantern-fish; swordfish; ramora; hagfish; angler; gar-pike; sturgeon; shark; sawfish; paddle-fish.

3. The variations, real or apparent, in the breathing habits of the porcupine-fish; the climbing-fish; the lung-fish.

4. Peculiarities in swimming as seen in the flying-fish; the flounder; the sea-horse.

5. Intensity of sound under water, and the corresponding structure of the fish's ear.

6. Light and sight under water (as in 5).

7. Protection of fishes: sting-ray; torpedo; coral-fish; sturgeon; lava-fish; swordfish; sawfish; pipefish.

8. The social instinct of fishes, and "schools."

9. The breeding habits of salmon; eel; stickle-back; sturgeon; whitefish; shark; sea-horse; sunfish.

10. The fishing industries of the Great Lakes or of the cold oceans, with a list of the fishes caught and their values.

11. Fish nets and traps: seine; gill-net; pound-net; trawl, French or English; fish-wheel; fish-weir; spear; dip-net; set-line; spoon; fly.

12. The U.S. Bureau of Fisheries: its locations, its problems, and its methods.

13. The State Fish Commission, as above.

14. Game and fish laws; their purpose and their enforcement.

15. Game fish of the fresh waters; trout, ba.s.s, pickerel, and muskellunge.

16. Game fish of the ocean: tarpon, tuna, sea-ba.s.s, swordfish, and bluefish.

17. Fish as food.

18. Fish diet and leprosy.

19. Fish diet and parasitic worms.

20. Fish nuisances: carp, catfish, and dogfish.

21. Commercial products of fishes, their preparation and their uses: caviar, s.h.a.green, cod liver oil, isingla.s.s, and glue.