ANIMAL LIFE GENERATION. 357 



geologic ages. Especially the Archaeop- 

 teryx, a fossil reptilian bird of the Mesozoic, 

 appears to furnish the best sample from which 

 the differentiation into Reptile and Bird took 

 start. But there are many other extinct speci- 

 mens of the same general kind known as 

 pterosauria. (3) Mammalia (udder-bear- 

 ing). Here the skeletal criterion is dropped 

 and the method of alimentation for the young 

 is taken. The difficulty with the classification 

 of Huxley is that it has no leading principle 

 of ordering the Vertebrates. A desperate at- 

 tempt to cling to the bones as the standard is 

 seen in the little-known divisions, Lyrifera 

 (Fishes and Selachians), Quadratifera (Rep- 

 tiles and Birds), Malleifera (Mammals), And 

 in this highest class, the Mammals, there is 

 found no small diversity of ordering from 

 Linneus till the present time. Still there is 

 good ground for dividing the Mammals as fol- 

 lows: Monotremata, oviparous (Ornitho- 

 rhyncus) ; Marsupialia, viviparous, with 

 pouch for young; Placentalia, having a pla- 

 centa with uterus. The last rise through a 

 variety of forms to the simian and finally to 

 man. 



The foregoing line of development shows 

 the ascent of the human species through what 

 we have named the total Generation of Ani- 

 mal-life. On the whole the basic principle of 



