72 



SYNGAMY IN PROTOZOA 



which unite in pairs. In the latter case, the individual which gives rise 

 to the gametes is known as a gametocyfe, and the process by which it gives 

 rise to the gametes as gametogony. 



The gametes which unite may be alike in size and shape, in which 

 case they are known as isogametes, and the process of union as isogamy. 

 On the other hand, they may be recognizably different from one another 

 in size or structure, and are known as anisogametes. The process is then 

 called anisogamy or heterogamy. If the gametes differ in size, the large 



Fig. 41. — Syngamt of Cercomonas longicauda { x ca. 2,000). 



1916.) 



(After Woodcock, 



1. Two individuals uniting by their posterior ends. 



3. Still later stage after nuclei have fused. 



4. Stage in which fiagella are lost and body rounded. 



2. Later stage in the union. 

 5. Encysted zygote. 



one is called the macrogamete and the small one the microgamete. It 

 usually happens that the small gamete or microgamete is actively motile, 

 on which account it is regarded as the male gamete, as it corresponds in 

 function with a spermatozoon of higher animals. The larger macrogamete, 

 which is usually a passive body heavily charged with food reserve material, 

 corresponds with the ovum. There is every transition between the process 

 of isogamy and anisogamy. Thus, in some cases the gametes are equal in 

 size, but differ from one another only in the size of their nuclei. In other 



