haeckel's anthropogenie. 245 



"The presence of the amnion in the vertebrate embryo is associated 

 with so many important peculiarities of organization, that all amniota 

 must be regarded as descended from a single ancestral form — the 

 lizard-shaped " protamnion," which was developed from an amphibian 

 form, probably in the carboniferous period, as we already meet with 

 certain, saurian remains in the permian formation. 



From the protamniata, which constitute the fifteenth evolutionary 

 stage, the sauropsida and mammalia diverge in two difierent lines, 

 and it is to the latter group that man certainly belongs. The ana- 

 tomical peculiarities of the mammalia necessitate their descent from 

 a common ancestral form (promammalia), one of the two branches of 

 the protamnia, and presenting an advance on the protamnia by the 

 peculiarities in skull and brain, the development of a covering of hair, 

 diaphragm, and of mammary glands. This advance must have taken 

 place in the triassic period, although it is not in the mesozoic age 

 that the mammals were most developed. Esj)ecially intei'esting is it 

 that the mammalian fossils of this age all indicate marsupial and 

 probably monotrematous animals. It is only in the tertiary period 

 that traces of placental mammals are found. Comparative anatomy 

 and ontogeny support the evidence derived from palaeontology. The 

 mammalia are divided by Blainville into the ornithodelphia (the 

 monotremes), the didelphia (the marsupial), and the monodelphia (all 

 other mammalia), and this coiTesponds to the order of appearance in 

 time. 



The sixteenth stage is formed by the monotremata, which still retain 

 the cloaca inherited by the protamnia, and are further characterized 

 by the absence of teats. Brain-skeleton, and indeed all the pecu- 

 -liarities of the anatomy of these animals, are inherited from the 

 protamnia. The absence of teeth must be regarded as secondary, 

 for the first traces of mammalia indicate the possession of teeth 

 (microlestes, dromatherium). The ornithodelphia and didelphia form 

 two widely diverging lines of descent from the promammalia, and it 

 is among the latter that we must look for the next stage of develop- 

 ment. The didelphia (marsupialia) of the present day are remark- 

 ably restricted in their distribution, but this was by no means the 

 case in. mesozoic and cainozoic times. Their anatomical peculiarities 

 are so characteristic for all, that they must be regarded as forming 

 one branch of the promammalian stem, and as the seventeenth stage 

 of evolution of man. The remaining stages, (eighteenth-twenty- 



