THE PHYLOGENESIS OF VERTEBRATES 45 



9. Insectivora (of the modern type, still quite primitive. 

 The rodents are valuable here also as collateral lines, 

 descended from the primitive Insectivora). 

 10. Lemurs (practically modern Mesodonta, and hence repre- 

 senting fairly well the immediate ancestors of the anthro- 

 poids). 

 :i. Ccrcopithecidoe (tailed monkeys of the Old World). 



12. The. large tailless apes of the Old World (Gorilla, Chim- 



panzee, Orang, Gibbon). 



13. Pithecanthropus (extinct). 



14. Homo primigenius (extinct). 



15. Homo sapiens. 



In this list an attempt has been made to enumerate only 

 living forms, specimens that are still available to the anatomist 

 for dissection and full comparison. In two cases, however, 

 13 and 14, this resolution was broken, owing to the vital 

 importance of these forms. It must also be remembered 

 that we possess at least a partial skeletal record of some of 

 the extinct groups that lie in the direct line of ancestry, and 

 that these records, although extremely fragmentary, are of the 

 utmost value. It will also be seen that these stages are not 

 those of coordinate groups, but that they grade from Classes 

 to Orders, then to Families, and finally to Genera and Species ; 

 this is, however, the natural manner of considering an an- 

 cestry, for the early stages are the less detailed and are ex- 

 pressed equally well by all the members of a large group, 

 while the finishing touches, which separate genera from ge- 

 nera and species from species, consist of slight differences, 

 more recent and superficial in character. 



A similar gradation is seen in the developmental history, 

 as studied in comparative embryology, in which the earliest 

 features laid down are those of the main subdivisions; then 

 come in succession those of the Class, the Order, the Family, 

 and so on until the distinguishing characters of the Species 

 make their appearance, the latter usually not fully expressed 

 until maturity. 



The truth of this actual recapitulation of the history became 



