60 SEX-LORE 



the other hand, there are instances where the two 

 combining cells differ in size and shape (Fig. 29). 

 We find a smaller agile one, which is called the male, 

 and a larger more immobile one, called the female. 

 The next stage is to be found in simple multicellular 

 animals forming a cell-colony, where some of the cells 

 become distinct from the other body cells and develop 

 into special cells that are alone capable of repro- 

 a 



FIG. 29. CONJUGATION OF ZANARDINIA. (After Reinke.) 

 a, Female; b, male ; c, conjugation ; d, product of conjugation. 



(From Delage, " 



ducing the species. These are called the sex cells 

 or germ cells; they develop into the new individuals 

 (Fig. 30). 



In the higher forms of reproduction the germs or 

 sex cells are gathered together in special organs called 

 the sex glands. There ar^ two kinds: the male sex 

 gland or testis, producing male germs or sperms (also 

 called spermatozoa); and the female sex gland or 

 ovary, producing egg cells or ova. As a rule, each 

 individual possesses only one kind of sex gland, either 

 male or female, and is accordingly called a male or 

 a female. The higher animals possess two sex glands 

 of the same kind, one at each side of the body. 



