28o THE DOCTRINE OF DESCENT. 



Sperm whales or cachelots (Physeteridae), and the last 

 members are the right whales (Balaenidse). This is 

 evinced by the fact that the whalebone or baleen plates 

 are developed only after the rudimentary teeth have 

 made their appearance in the jaws of the embryo, a 

 heritage from the profusely and persistently toothed 

 ancestors. 



In the Lemuridse, the system unites the heterogeneous 

 remains of a collection of animals which, by reason of 

 their prehensile hind feet with their opposable hallux, 

 were regarded as fellow-members of the order of 

 " true apes." The connecting link is not their anato- 

 mical constitution — they diverge widely in the form of 

 the skull and in dentition — but rather their geographi- 

 cal distribution, restricted to Madagascar and a few 

 advanced posts of Asia. Undue influence has also 

 been allowed, certainly very unscientifically, to a certain 

 peculiar outlandish impression which they make upon 

 the observer. The constitution of their skull refers 

 them to a very low grade in the scale of the mammalia. 

 If we view them as a whole, they exhibit no general 

 relations with any particular order of mammals, but, 

 according to the individual genera, point to those orders 

 which, like themselves, possess discoidal placenta ; the 

 majority of reasons favour the hypothesis that the 

 Lemuridas now living are the last and little modified 

 offshoots of a division of mammals at one time far 

 more richly developed, and that Rodents, Insectivora, 

 Cheiroptera, and Apes, are twigs of this great branch. 



The Rodents are particularly interesting, because, in 

 conjunction with stubborn persistency in the very cha- 

 racteristically constituted dentition, accompanied by 



