ILLUSTRATIONS. 



PLATE. 



y-Age 

 Plate I. Diagram illnstratiiig the network of descent, succession of genera- 

 tions, alternating piiases, and expansion of the fertihzed egg 26 



TEXT FKiURES. 



Fi(i. 1. Diagram showing the different types of cell structures and their posi- 

 tion in the life history of organisms 18 



2. Diagram showing the relative importance of the paragamic, ai)aylo- 

 ganiic, and haplogamic phases in the life history of various groups 

 of organisms 18 



8 



