74 



THE LOBOSA 



In the case of Endamoeba coli (Schaudinn [36]), for example, 

 the uninucleate amoeboid form discharges all foreign bodies from 

 its cytoplasm and becomes surrounded by a clear, soft, jelly-like 

 envelope. Within the cyst-wall it divides into two equal parts 

 each with a single nucleus, and these two parts remain separate 

 for a considerable time. The two nuclei then fragment, their 

 chromatin being scattered in the cytoplasm as isolated chromidia. 

 The two nuclei are now reconstructed, but each reconstructed 

 nucleus is relatively poor in chromatin. Each of these nuclei now 

 divides into two by a primitive kind of mitosis ; one of them from 

 each half-amoeba is rejected as a polar nucleus and the remaining 

 one divides again. At this stage in the process the protoplasm 

 contracts, the gelatinous membrane disappears, and the cyst 

 is surrounded by a harder membranous wall. The daughter 

 nuclei of this mitosis conjugate reciprocally with the daughter 

 nuclei of the other half-amoeba, and each of the two zygote nuclei 

 thus formed divides twice. The eight nuclei thus formed become 

 the nuclei of eight amoebulae which escape from the cyst. 



In Amoeba proteus also, according to Scheel, division of the 

 nucleus and cytoplasm takes place during the encystment, and 



FIG. 9. 



A, cyst of Amoeba proteus ; abc, cyst-wall ; d, gelatinous envelope ; K, F, nuclei ; 0, albu- 

 minous bodies, x 300. (After Scheel.) B, cyst of Endamoeba blattae, with 25 nuclei. (After 

 Schubotz.) 



a swarm of small amoebulae emerge from it when the cyst breaks 

 down. In this case, however, there is no evidence that any form of 

 nuclear conjugation takes place during the encystment. 



Conjugation. Although the complete life-history of only a few 

 species of the Lobosa has, at present, been fully worked out, the 

 evidence is accumulating to justify the conclusion that a process of 

 conjugation is an essential condition for the completion of the life- 

 cycle in all forms. The process of conjugation has not yet been 

 observed in Amoeba proteus or in any of its allies. Nuclear con- 

 jugation accompanied by fusion of the cytoplasm occurs during, 

 encystment in Endamoeba coli. 



