PROTOZOA IN GENERAL 87 



these two types of sex cells unite, a zygote is formed from which a new 

 colony may arise. The macrogametes may also show a type of sexual 

 reproduction ^\^thout fertihzation. When this occurs, they remain 

 ^^dthin the colony, increase in size, divide into many cells, and finally 

 escape to form new colonies. These groups of cells are known as parthe- 

 nogonidia (Fig. 30 E). In many of the Sporozoa there are both sexual 

 and asexual generations. The zygotes produce a number of spores which 

 develop into sporozoites. These become nutritive individuals, or tro- 

 phozoites, and these in turn may form another generation of gametes. 



