REPRODUCTION 233 



ultimately become a mere cyst wall containing large numbers of 

 encysted young. A quite different type of internal bud called a 

 "gemmule" is formed in Sphaerospora dimorpha according to Davis 

 (1916). These correspond to the agamont buds of the gregarines 

 (Fig. 121). 



m. MULTIPLE DIVISION (SPORE FORMATION). 



In reproduction by multiple division the entire protoplasm breaks 

 up simultaneously into a brood of minute young, a mere fragment 

 with perhaps a residual nucleus, may be left unused. Although the 

 end-product may be the same there is a difference in principle 

 between rapidly following divisions of cells within a cyst (as in 

 Colpoda cucullw) and the fragmentation of a cell into many minute 

 cells. There is less difference between sporulation and multiple 

 endogenous budding as in Schizocystis or Eleutheroschizon described 

 above. 



Multiple division in many cases results in the formation of a 

 brood of smaller cells which develop directly into organisms similar 

 to the parent. In other cases the representatives of the brood are 

 differentiated as gametes, and fertilization is necessary before devel- 

 opment begins. We thus distinguish between sexual and asexual 

 generations of spores, a distinction mainly characteristic of parasitic 

 forms, but typical of many free-living types as well. In still other 

 cases multiple division may follow immediately after fertilization, 

 a phenomenon which is highly developed in the Sporozoa where the 

 ultimate products of division — sporozoites have a renewed poten- 

 tial of vitality. 



Multiple division or spore formation thus may occur either in the 

 agamont (asexual) phase, or in the gamont and zygote phases 

 (sexual) of the life cycle. Division, budding or sporulation in the 

 asexual phase is called agamogony ( = schizogony) ; in the sexual 

 phase gamogony ( = sporogony). In the great majority of Protozoa 

 the two phases together in an alternation of generations, make up a 

 complete life history. 



In Mastigophora sexual processes have in no case been safely 

 established, multiple division when it occurs being agamogony. In 

 animal flagellates, however, particularly the parasitic forms, a 

 highly characteristic method of multiple division is widely dis- 

 tributed. Here in certain phases or under conditions not yet well 

 understood, trypanosomes, trichomonads, lophomonads and other 

 parasitic flagellates undergo a process of asexual sporulation to 

 which the specific term "somatella formation" has been applied. 

 It is well described by Minchin and Thompson (1915) in the case 

 of Trypanosoma lewisi (Fig. 122) as follows: 



"The parasites when taken up by the flea (Ceratophyllus fasciatus) 



