V. 



ON CERTAIN MODIFICATIONS IN THE 

 STRUCTURE OF DIVING ANIMALS. 



In this communication the Cetacea, in the class Mammalia, were 

 contrasted with the Phocidae, and in the class Aves, the Colymbidae 

 were contrasted with the Cinclidae, as to the degree of modification 

 which their tegumentary, circulatory, and osseous systems had 

 undergone in adaptation to their aquatic habits. 



The skin of the seal was less specially modified than that of the 

 whale, and the aberrations from the ordinary mammalian characters 

 which its bones and teeth presented were in like manner less 

 marked than those of the animals with which it was compared. 

 The teeth in the order Seals were often irregular as regarded their 

 number, their implantation, and their permanence in the jaw; and 

 the epiphyses of the vertebrae were often slow to unite with the 

 bodies. All these particularities were instances of correlation of 

 growth existing between the skin and systems as far removed from 

 its direct influence as the osseous and dental ; and all these parti- 

 cularities, together with those of the systems with which they 

 were correlated, were much more marked in the whales than in the 

 seals. The seals were well provided with intra-hepatic venous 

 sinuses, but their reservoirs for arterial blood were far inferior in 

 grade of development to those of the cetacea. Little could be said 

 as to difference in the degree of patency in the foramen. ovale and 

 ductus venosus in the two subjects of comparison, at least so far as 

 the common seal (P/ioca vitidina) and common porpoise (P/wcaena 

 communis) might serve as representatives of the two orders. To 

 the rudiments of the foetal vena umbilicalis and ductus Botalli, in 

 both, the same remark applied. 



The stunted salivary glands of the seals seemed an approximation 



