II.] 



INCIPIENT STRUCTURES. 



53 



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, consist- 

 ing of some of the constituent fibres of the 

 horny plates which, as it were, fray out 

 and the mouth is thus lined, except below, 

 by a net-work of countless fibres formed by 

 the inner edges of the two series of plates. 

 This net-work acts as a sort of sieve. When 

 the whale feeds it takes into its mouth a 

 great gulp of water, which it drives out 

 again through the intervals of the horny 

 plates of baleen, the fluid thus traversing the 

 sieve of horny fibres, which retains the mi- 

 nute creatures on which these marine mon- 

 sters subsist. Now it is obvious, that if this 

 baleen had once attained such a size and de- 

 velopment as to be at all useful, then its pres- 

 ervation and augmentation within service- 

 able limits would be promoted by " Natural 

 Selection " alone. But how to obtain the 



FOUR PLATES OF 



BALEEN SEEN 



OBLIQUELY FROM 



WITHIN. 



