190 GERM-CELL CYCLE IN ANIMALS 



All the species of Metazoa may be separated into 

 two groups. The individuals in one group of species 









Fig. 56. — Diagram of the reproductive organs of the earthworm, dorsal 

 view. A, B, C, seminal vesicles ; N, nerve-cord ; O, ovary ; OD, ovi- 

 duct ; R, egg sac ; S, spermatheca ; SF, seminal funnel ; T, testes ; 

 VD, vas deferens. {From Marshall and Hurst.) 



possess only one sort of reproductive organs (male or 

 female) and produce only one sort of germ cells (eggs 

 or spermatozoa) ; these species are said to be dice- 



