Mammals to Aquatic Life. 163 



namely that the ancestors of the toothed whales were terres- 

 trial animals with a dermal armature. It follows from this 

 that on the one hand a great gulf is fixed between the whale- 

 bone and the toothed whales, and that on the other we must 

 relinquish all attempts at bringing the toothed whales into 

 any close relation whatsoever with the Ungulates or the 

 Carnivores. The toothed whales branched off from terrestrial 

 ancestors at a time when the latter still possessed an exo- 

 skeleton of epidermic scales, such as, for instance, a division 

 of the Edentata still bears as, perhaps, an ancient heirloom. 

 I would here like to quote a statement made by Baume when 

 discussing the question whether the carapace of the armadillo 

 is or is not acquired : — " There is nothing to prevent us 

 from deriving the Mammalia, including even the Placentalia, 

 from armour-bearing ancestors " *. 



As a new instance of adaptation to the aquatic life we have 

 now learnt to recognize the gradual disappearance of the 

 dermal armature of terrestrial ancestors. It is not only in 

 the group of toothed whales that this is seen ; we already find 

 the same phenomenon at an earlier period of the earth's 

 history. It is assumed by recent investigators that the Ichthyo- 

 sauri, which were pelagic animals, sprang from land-inhabiting 

 reptiles. According to Fraas f the epidermic exoskeleton has 

 disappeared in these creatures, with the exception of remains 

 of horny scales, which are to be found on the anterior margin 

 of the paddles (as in JSeomeris). " The integument of the 

 Ichthyosaurus , as has been clearly proved by our discoveries, 

 was a completely naked and deeply pigmented skin, for the 

 most part entirely without an armature of scales, whether 

 horny or bony plates, with the exception of a region on the 

 front margin of the paddle, which was protected by a longitu- 

 dinal row of horny scales." 



A more perfect analogy could hardly be found. On the 

 one hand in the reptiles, on the other in the mammals, the 

 dermal armature has been lost owing to adaptation to the 

 aquatic life ; in both cases it persists in a vestigial condition 

 on the anterior margin of the flippers. The reason why the 

 remains of the armature should have persisted so long at pre- 

 cisely this point is readily understood when we reflect on the 

 speed with which these animals cleave the water and the 

 necessity for keeping these parts of the body rigid. 



The comparative examination of the integument of the 

 aquatic mammals proved to us how it was possible for resem- 



* Baume, ' Odontologische Forscbungen,' Leipzig, 1882, p. 197. 

 t E. Fraas, " Ueber die Finne von Ichthyosaurus" Jabreshefte Ver. far 

 Vaterl. Naturkunde in Wiirttemberg, 1888. 



