28o THE DOCTRINE OF DESCENT. 



(Physeteridas), and the last members are the right whales 

 (Balaenidae). This is evinced by the fact that the whale- 

 bone or baleen plates are developed only after the ru- 

 dimentary teeth have made their appearance in the jaws 

 of the embryo, a heritage from the profusely and per- 

 sistently 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 anatomical con- 

 stitution — they diverge widely in the form of the skull 

 and in dentition — but rather their geographical distribu- 

 tion, restricted to Madagascar and a few advanced posts 

 of Asia. Undue influence has also been allowed, cer- 

 tainly 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 in- 

 dividual genera, point to those orders which, like them- 

 selves, possess discoidal placenta; the majority of rea- 

 sons favour the hypothesis that the Lemuridae 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 

 characteristically constituted dentition, accompanied by 

 several peculiarities of skull, they manifest the most ex- 



