PRIMITIVE AMNION ANIMALS. 1 33 



a fossil Man dating from the Deluge ! (" Homo diluvii 

 testis." 154 ) 



As the vertebrate form occurring in our pedigree imme- 

 diately after these Batrachian ancestors — and, therefore, as 

 the fifteenth stage — let us now examine a lizard-like animal, 

 of which no fossil remains have been obtained, and which 

 is not even proximately represented in any extant animal 

 form, but the former existence of which we may infer with 

 the utmost certainty from certain comparative anatomical 

 and ontogenetical facts. This important animal form we 

 will call the Protamnion, or Primitive Amniotic animal. 

 All Vertebrates higher than the Amphibia — that is, the three 

 classes of Reptiles, Birds, and Mammals — are so essentially 

 distinct in their whole structure from all the lower Verte- 

 brates which we have as yet considered, and, on the other 

 hand, have so much in common, that we may class them 

 together in one group as Amnion Animals (Amniota). It is 

 only in these three classes of animals that we find that 

 remarkable envelope of the embryo known as the amnion. 

 (Cf. vol. i. p. 386.) The latter must probably be regarded as 

 a kenogenetic adaptation, as caused by the sinking of the 

 embryo into the yelk-sac. 155 



All known Amnion Animals, all Reptiles, Birds, and 

 Mammals (Man included), coincide in so many important 

 points of organization and development that we are fully 

 justified in asserting their common descent from a single 

 parent form. If the testimony of Comparative Anatomy 

 and Ontogeny is entirely unquestionable in any point, it is 

 certainly so here. For all the special peculiarities and 

 characters, which appear accompanying and following the 

 formation of the amnion, and which we found in the 



