190 GERM-CELL CYCLE IN ANIMALS 
All the species of Mrrazoa may be separated into 
two groups. The individuals in one group of species 
Fic. 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; 7’, 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 dioe- 
