332 



ANIMAL BIOLOGY 



with the phenomenon of sex. We have already described 

 some of the manifestations of sex in the conjugation of 

 Paramcecium where after a series of generations produced 

 by fission there is a union of individuals by pairs, during 

 which each individual receives a nucleus from the other. 



FIG. 226. Volvox aureus. (After Klein and Schenck.) A, mature 

 colony containing daughter colonies; () and ova (o); B, group of 32 de- 

 veloping spermatozoa seen end on; C, the same seen sideways; D, mature 

 spermatozoa, X 824. 



After the union of one of its own nuclei with the one re- 

 ceived from its partner, the individuals separate and con- 

 tinue^ to divide by fission as before. More commonly 

 in primitive organisms there is a complete fusion of nucleus 



