236 



GENERAL BIOLOGY 



The record of this study will consist in the two completed 

 tables just outlined, together with a few brief statements as 

 to the relative uniformity or divergence of the appen- 

 dages of particular segments or particular regions of the 

 body, with possible reasons therefor. 



Divergent development has already been illustrated by 

 both the major and the minor series of forms that we have 



been consider- 

 ing. Indeed, in 

 all these, but es- 

 pecially in the 

 two main series, 

 the divergence is 

 greater than has 

 been specifically 

 pointed out; for 

 the lower types 

 in each series 

 represent in 

 themselves the 

 termini of their own lines of development, and not mere 

 passing stages to higher forms. The table of classification 

 on page 221 is but a statement of the main lines of 

 divergence. 



Phylogeny. — The forms of a single line of descent consti- 

 tute a race, or a phylum. The study of phyla is called phylo- 

 geny. A common device for expressing gra phically one's con- 

 ception of phylogeny is the so-called "genealogic tree." The 

 generalized forms are placed near the base of the tree, the 

 specialized forms, out at the tips of the longest branches, 

 and the intermediates are arranged, according to one's con- 

 ception of relationship , somewhere in between. The student 

 who has done the work of the last two practical studies will 



Fig. 145. Gammarus fasciatus (after Paulmier). 



