660 , THE POPULAR SCIENCE MONTHLY. 



better illustrated by certain worm-like animals which live in the 

 stomachs of sharks and other fishes. Being placed where food is 

 ground up fine and all ready for assimilation, there is no need of 

 a mouth, and but little need of a stomach, so both of these organs 

 are lost, and all food is absorbed into the system through the outer 

 walls of the body. Eyes are also lost, and the animal becomes a 

 mere stomach ; but, as for that matter, most animals are a mere 

 stomach, with a few necessary organs to assist it. Some true fishes 

 can be classed as parasites, while many use other animals as a means 

 of attachment and protection. Under the dome of the true bell- 

 shaped jelly-fish, a species of fish is generally found that is never 

 taken under other conditions. It appears not to be affected by the 

 stinging cells of the animal, but will stay near the mouth while 

 the darts are exerting their deadly powers upon some brother- 

 fish, and after this fish is dead will pick up enough for a meal from 

 what the jelly-fish does not eat. What benefit this fish is to the 

 jelly-fish it would be impossible to say, but in such cases some 

 service is usually returned, such, for example, as that of warning 

 the friend in case of danger. This habit of commensalism, or 

 eating at the same table, is seen in other animals, as the oyster- 

 crab, pilot-fish, and others. They seem to recognize their friends, 

 and not only do not harm but even protect them. The oyster- 

 crab could, if so inclined, devour the oyster without trouble, but 

 it never offers to. Under such conditions certain apparently dead- 

 ly powers have no effect, and these animals may even be entirely 

 unharmed by digestive fluids. Fish are sometimes found in very 

 odd places. One burrows into the side of a larger fish and stays 

 there, as in a house, catching what food passes by. Another fast- 

 ens itself on to the sides of a fish by means of a sucker, and, assum- 

 ing a similar color to that of the larger one, is easily overlooked 

 by its enemies. One of these, the lump-fish, is a very pretty green 

 in color. There are certain fishes that always stay in the surf 

 near shore, being able to remain there without being cast ashore, 

 and never seeking quiet water. 



Among the patches of sea-weed which float in the Gulf Stream 

 there are numerous small fishes very prettily colored. One among 

 these has a curious mode of defense, and because of this is called 

 the file-fish. Normally folded down upon its back is a rather 

 long spine. Whenever danger is apprehended, this spine suddenly 

 springs upright, and is held there by a little bone behind it near 

 the base and under the skin. If this bone is touched with a knife, 

 it can be pressed down, and then the spine will fold back ; but, 

 unless the bone is removed, the spine will remain rigidly upright. 

 The fish possesses the power of raising or lowering the spine at 

 will. We sometimes see flying-fish jump out of the water and 

 scale along the surface for many feet. Chased by their enemies. 



