SCHIZOGONY 



65 



by the large form, which apparently has ceased to grow, so that eventually 

 its entire cytoplasm is used up in the production of a number of small 

 forms. At each division there is a nearer approach to equal binary 

 fission. It is evident that such a method of division approaches a budding 

 process. 



Binary fission usually occurs in the free-living state, and as the division 

 is taking place the organism may be actively motile. Amongst the 

 Rhizopoda, the amoebae are frequently perfectly quiescent while binary 

 fission is proceeding. In some cases, binary fission takes place in the 

 encysted condition. This appears to be the normal method of multiplica- 

 tion of species of Colpoda. The organism secretes a cyst in which it 



Fic. 38. — Colpoda steini : Multiplication of a Single Indivibual during a 

 Period of Seven Hours' Observation ( x 650). (Original.) 



A. Ciliate about to encyst. B. Encysted ciliate. 



C. Division into two completed: commencing division into four. 



D. Four daughter ciliates in cyst. 



E-G. Escape of ciliates through rupture in cyst wall. 

 H. Crumpled cyst after escape of ciliates. 



divides into two, each of which again divides (Fig. 38). The four daughter 

 ciliates then rupture the cyst and swim away. Similar divisions within 

 cysts occur amongst the Rhizopoda and Mastigophora (Fig. 143). 



SCHIZOGONY. — By this term is understood a method of multiplica- 

 tion which occurs typically amongst the Sporozoa (Fig. 39). As the 

 organism is growing, repeated divisions of the nucleus and daughter 

 nuclei take place, till finally there may be present a large number of nuclei 

 in a single mass of cytoplasm. The number of nuclei produced varies 

 considerably, and may be as few as four or as many as a hundred or more. 

 The nuclei arrange themselves on the surface of the cytoplasm, which 

 becomes raised into a series of elevations, into each of which a nucleus 



I. 5 



