VERTEBRATE ANCESTORS OF MAN ? 63 



beginning of the Mesolithic or Secondary time per- 

 haps already from the Permian period of the Primary 

 time. 



The Protamnia were the common stem, from 

 which were evolved in two diverging branches, 

 Reptiles and Birds on the one hand, and Promam- 

 malia on the other. With the Promaminalia only 

 we have to do as ancestors of man. 



Among our forefathers, from the sixteenth to the 

 twenty-second stage, we are, says Haeckel, more at 

 home, as they all belonged to the great and well- 

 known class of Mammalia. The now long extinct 

 and unknown common stem-form of all Mammalia, 

 which Haeckel designates by the name of Promam- 

 mal, stood nearest the Ornithorhyncus and Echidna 

 of all now living animals. 



Promammalia were evolved from Protamnia 

 probably in the Triassic period of the Mesolithic 

 or Secondary time, by ' increased development of 

 the internal organisation,' by the formation of a 

 lacteal gland to supply milk for the nourishment of 

 the young, and by the conversion of epidermic scales 

 into hairs. 



Marsupialia, or animals of the Opossum and 

 Kangaroo, tribe, constitute the immediate transition 

 between the Monotremata and Placental Mammalia 

 as well in an anatomical as in an ontogenetical and 

 phylogenetical respect. Among the marsupialia, 

 therefore, ancestors of man must also have been 

 found. They originated from the Promammalian 



