32 THE INVERTEBRATA 



cycle fission may take place in any of the modes described above, and 

 that the agamogony of a species may proceed in more than one of 

 these ways (as, e.g., that of Amoeba proteiis by binary or multiple 

 fission) ; (2) that in the cycle of most protozoa there is a point at which 

 adjustment must be made to unfavourable conditions, either re- 

 curring in the local habitat or met with in the course of the distribu- 

 tion of the species (e.g. freshwater forms and parasites); and that at 

 this time {a) the ordinary agamogony is suspended, {b) the syngamy, 

 if any, usually takes place, {c) there is often a phase of protective 

 encystment, {d) there is often very rapid multiplication by multiple 



[•j Agamont (Schizont, Meront) 



/ \ Agamogony (Schizogony, Merogony) 



AgamQtes (Schizozoites, Merozoites) 



/ \ Growth of Agametes 



( J \) Agamont of second generation 



Agamogony repeated 



r7\ riS Gamont 



X \ X \ Gamogony 



^S§^ S$8^ Gametes 



\ / Syngamy 



a 



Zygote (Sporont) 

 Sporogony 

 ©'0000©©® Sporozoites 



/ 

 



Growth of sporozoite 

 Agamont 



Fig. 29. A table of the life history of a protozoon. 



or repeated fission, which may be the sporogony, the gamogony 

 (eugregarines), or an agamogony; (3) that any part of the cycle may 

 be omitted ; in such cases it is most often the sporogony which is 

 dropped, but many species appear to omit gamogony, and in a few 

 (e.g. Monocystis and the other eugregarines) there is no agamogony; 

 (4) that a reduction division may occur at either of two points in the 

 cycle — shortly before syngamy (most cases), or directly after the 

 formation of the zygote (the Telosporidia and Volvocina), and that 

 correspondingly either the diploid or the haploid phase may extend 

 over the greater part of the life history. 



