II.] 



INCIPIENT STRUCTURES. 



45 



fishes up to man, there being always an anterior pectoral 

 pair placed in front of a posterior or pelvic pair when both 

 are present, and in no single instance are there more than 

 these two pairs. 



The development of whalebone (baleen) in the mouth of 

 the whale is another difficulty. A whale's mouth is fur- 



MOUTH OF A WHALE. 



nished with very numerous horny plates, which hang down 

 from the palate along each side of the mouth. They thus 

 form two longitudinal series, each plate of which is placed 

 transversely to the long axis of the body, and all are very 

 close together. On depressing the lower lip the free outer 

 edges of these plates come into view. Their inner edges 

 are furnished with numerous coarse hair-like processes, 



