234 PISCES. 



continued from it as a short infundibular tube, but frequently only 

 its commencement, or the pharynx, is developed, which then forms 

 an extremely short canal, which is surrounded throughout its entire 

 length by an annular layer of muscular fibres. There being no 

 larynx in Fishes, the oesophageal intestine is attached to the verte- 

 bral column arid pericardium by cellular tissue. A dense mucous 

 membrane, frequently beset with tubercles and papillary projections, 

 lines the oesophagus, and is usually disposed in coarse longitudinal 

 folds, that are frequently continued into the stomach. 



There are Fishes in which the intestinal tube is continued from 

 the pharynx without any indication of a gastric enlargement or of 

 convolutions, and with which no organ of secretion is connected, 

 except the liver. It is interesting to commence with such simple 

 structures and ascend to the more complex. 



The greatest departure from the structure of the Yertebrata gen- 

 erally, and also from that of Fish, is furnished by the anomalous 

 genus Amphioxus. Its internal branchial cavity is prolonged into 

 a narrow canal, the oesophagus, which is continued into a much 

 wider intestine. The latter is always of a green color, as is also a 

 caecum that is developed from it. The green fluid or gall is secreted 

 by a glandular layer situated in the parietes of the intestine, and 

 which, as in many Annelides, has not yet freed itself from the intes- 

 tine in the form of a more highly organized parenchymatous liver. 

 The green-colored portion terminates by an abrupt line, and then 

 the walls of the intestine present, as do those of the caecum also, 

 their natural translucency and delicate texture. The intestinal sac 

 exhibits, upon the whole of its internal surface, a glistening epithe- 

 lium and an active vibratory or twinkling movement that hitherto 

 has not been observed in any other vertebrated animal. This re- 

 markable fish appears to be nourished simply by swallowing the 

 microscopic animalcules met with in the sea-water. Nevertheless, 

 excrements are extruded from the body of a dark color and stringy 

 form. 



Devoid of convolutions, and without any special dilatation for the 

 stomach, if we except a slight increase in its width at one particular 

 part, the intestine runs straight from the mouth to the anus in the 

 Cyclostomi, e. g., Petromyzon, in Myxine, where, however, it is 

 wider, in Syngnathus, and in Chimaera, so that such is its condition 

 in the most different orders. In many other Fish, as the Cyprini and 

 Labri, in which the intestinal canal is long and spirally contorted, a 

 special gastric dilatation is also absent, while in others that are fur- 



