280 THE DOCTRINE OF DESCENT. 
sperm whales or cachelots (Physeteride), and the last 
members are the right whales (Balenide), 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 Lemuridz, 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 
Lemuride 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 
