VERTEBRATE ZOOLOGY. 463 



common catfishes of the northern hemisphere. All these 

 come to the surface to breathe and take in a fresh supply 

 of air. Three modifications are noticed. 



(1) In Ilypostomus, it is that portion of the intestinal 

 canal immediately behind the stomach that is specialized. 

 " Here the mucous membrane entirely loses its ordinary 

 character, being devoid both of villosities and of glands, 

 and, therefore, no longer suited for absorption or secretion. 

 The walls of this portion contain a rich plexus of blood-ves- 

 sels, supplied partly from the aorta, but partly also by a 

 vein bearing blood from the remainder of the intestine. 

 After circulating through the plexus, and undergoing aera- 

 tion, the blood is returned, as usual, into the portal vein." 



(2) In Doras, the respiratory portion of the intestinal 

 canal is provided with villosities and not with glands. 



(3) In Callichthys, it is the posterior extremity of the in- 

 testinal canal that is modified for respiratory purposes, and 

 in this genus the impure air is expelled through the anus, 

 and not through the mouth, as in the other forms. 



In still other types than those studied by M. Jobert, the 

 modification for aerial respiration is manifested in the de- 

 velopment of peculiar diverticula or offshoots from the 

 pharynx, as in Ophioccphalus, Saccobranchits, and Amphip- 

 nous. 



The special interest attached to these facts arises from 

 the manifold ways in which the same physiological func- 

 tion may be exercised, and the susceptibility of so many 

 different parts to the assumption of the same office. The 

 lungs themselves, be it remembered, are merely a develop- 

 ment of the air-bladder, and this, doubtless, originated as a 

 simple diverticulum of the intestinal canal. In this connec- 

 tion, too, it is interesting to recall that some years ago Fritz 

 Miiller demonstrated in the land-crabs of Brazil analogous 

 variations in the modifications for aerial respiration that 

 is, each form was shown to be adapted for life on land by 

 diverse modifications of homologous parts, or by a peculiar 

 modification of a certain part. 



It may be well to add that some portions of M. Jobert's 

 work should be revised, as in the case of the Erythrinines. 

 It was long ago shown that in the typical Erythrini, the an- 

 terior part of the hinder compartment of the air-bladder was 



