I 



CHAPTER II.— PHYLOGENY. 



I. GENERAL PHYLOGENY. 



'T^HE actual phylogeny or genealogy of organisms 

 X can only be positively determined by paleonto- 

 logic research. We have been able in this way to ob- 

 tain numerous lines of descent of animals and some 

 general results as to the genealogic relations of the 

 primary types of animals and plants. Many forms of 

 both animals and plants are and have been without 

 those hard parts which are susceptible of preservation 

 in the formations of the earth's crust, so that no trace 

 of their existence remains to us. In these cases our 

 resort is embryologic investigation, since the embry- 

 onic history is a more or less complete recapitulation 

 of the types of the past ages, from which the existing 

 ones are descended. But since many representatives 

 of the ancient and primitive forms of life still remain 

 on the earth, we can trace, by the study of their struc- 

 ture, the larger features of general phylogeny. So far 

 as we have compared the results derived from these 

 three lines, it has been found that they coincide in 

 their indications. We have in this a satisfactory proof 

 that our conclusions are trustworthy contributions to 

 the knowledge of the history of life. 



The study of phylogeny shows that the evolution 



