236 BIOLOGY OF THE PROTOZOA 



by Davis (1916) are specialized reproductive centers in each of 

 which one or more sporoblasts are formed. In the same living 

 parent organism internal buds in various stages of maturity may be 

 present and in some cases the amoeboid parent organism may 

 uhimately become a mere cyst wall containing large numbers of 

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

 "gemmule" is formed in Si)hcerospora dimoryha according to Davis 

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

 and leave the cell in much the same way as do the buds of Council- 

 mania (Fig. 116). 



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 cvcuUvs) and the fragmentation of a cell into many minute 

 cells. There is less difference between sporulation and multiple 

 endogenous budding as in Schizocysfis 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 with the exception of the highly differentiated 

 Phytomastigida, sexual processes have in no case been safely estab- 

 lished, multiple division when it occurs being agamogony. Many 

 of the Euglenida in the Palmella stage have been described as giving 

 rise to a multitude of spores, but such cases are more probably 

 examples of repeated cell division under the protection of cyst 



