4(5 



THE GEXESrS OF SPECIES. 



[Cmap. 



W 



coiisistiiifj of some of the constituent fibres of tlie lioinv 

 plates — wliich, as it were, fray out, and the 

 luoutli 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 trreat 

 gul}) of water, wliich it drives out again 

 through the intervals of the horny plates of 

 baleen, the fluid thus traversing the sieve of 

 hornv fibres, which retains the minute crea- 

 tures on which these marine monsters sub- 

 sist. Xow it is obvious, that if this baleen 

 had once attained such a size and develop- 

 ment as to be at all useful, then its preser- 

 vation and augmentation within serviceable 

 limits would be promoted by "JS'atural 

 Selection " alone. But how to obtain the be- 

 ginning of such useful development ? There 

 are indeed certain animals of exclusively 

 aquatic habits (the dugong and manatee) 

 which also possess more or less horn un the 

 palate, and at first sight this might be taken 

 as a mitigation of the difficulty ; l)ut it is not 

 so, and the fact does not helj) us one stej) 

 iurtlier along the road : for, in the first ])lace, 

 these latter animals differ so materially in structure from 

 whales and porpoises that they form an altogether distinct 

 order, and cannot be thought to approximate to the whale's 

 progenitors. They are vegetarians ; the whales feed on 

 animals ; the former never have the ribs articulated in the 

 mode in -which they are in some of the latter; the former 



'/'•.'I 



i 



foCr plates of 



baleex seen 

 obliquely frum 



WITHIN. 



