AMERICAN INSTITUTE. 4^5 



And I am, therefore, led to believe that they swallow air, which 

 is no doubt decomposed in the usual manner in the alimentary 

 canal, affecting favorably the blood vessels as brought in contact 

 with them, precisely as in ordinary respiration among animals. 

 Their blood is likewise serated whenever they raise their scales, 

 and I think this is the case, more or less, with all fish. We know 

 that the blood cannot be brought to the air; therefore, nature 

 carries the air to the blood, by a wonderful system of ramified 

 continuous vessels, known as trachese, which are eternally 

 engaged distributing atmospheric air to S.11 parts of the body. 

 The tracheae, by a singular mechanism, are always kept pervious, 

 being constructed of three layers; the internal and external are 

 membranous, but the interior one is formed of an elastic thread, 

 coiled in a cylinder, which keeps the tube expanded, and con- 

 sequently full of air. 



The organs of smell in this fish, as well as others, are placed 

 in cavities on each side, in front of the head; they are blind sacs, 

 and do not communicate at all with the mouth or thorax; they 

 have two external openings to each sac, the entrance of which is 

 furnished with a valve, formed by a moveable membrane. I 

 have not been able to discover any organs of smell in the oyster, 

 clam or muscle, but in the snail I have. By placing the oil of 

 turpentine in their vicinity, they immediately indicate tlieir dis- 

 pleasure by withdrawing into their shell.* The hassar, as well 

 as all other inhabitants of the water, have no external ear. The 

 passage leading to the tympanum is a winding tube, composed of 

 cartilage instead of bone, and the external orifice, even in the 

 dolphin, is only large enough to admit the point of a small pin, 

 showing plainly that these important structures are calculated for 

 preventing the entrance of water in undue quantities into the 

 vestibule. The same care is shown in all departments of the 

 animal economy. The external ear of the hippopotamus is fur- 

 nished with a valve, composed of a membrane, ever capable of 

 closing the outward opening of the meatus, and thus preventing 

 the introduction of water when he feeds at the bottom of rivers. 



• I once cut the head of a snail off, and in a few Jays it was reproduced ; also, the fina 

 of fish, and they were renovated. 



