236 FAMILY: AMCEBID^ 



Multiplication takes place by binary fission (Fig. 110, 2 and 3). In 

 nuclear division the large chromatin granules separating the two nuclear 

 zones are replaced by smaller granules, and these arrange themselves 

 in the form of a band across the nucleus, which becomes elongated. The 

 band then divides into two clusters of chromatin granules, which pass 

 to opposite poles of the nucleus. The latter now becomes hour-glass- 

 shaped, and finally divided into two. The chromatin of each daughter 

 nucleus then arranges itself as granules between the two zones, as occurred 

 in the parent nucleus. Division of the cytoplasm then takes place. 



After a number of divisions of this kind, according to Mercier (1910) 

 a sexual phase is initiated. The amoebse which are to enter on this stage 

 of development are 40 to 50 microns in diameter, and though the cyto- 

 plasm is highly vacuolated there are no food inclusions. The nucleus, 

 which at first has the structure described above, changes its character. 

 Some of the chromatin in the intermediate zone is extruded from the 

 nucleus, while the nuclear membrane becomes much thinner. At the 

 centre there appears a large karyosome made up of an achromatic material 

 impregnated with chromatin granules, while a centriole can be detected 

 at the centre. The nucleus elongates, and from the karyosome there is 

 formed an intranuclear spindle with a centriole at each pole. The 

 chromatin granules upon the spindle fibres become separated into two 

 groups, which collect at each pole of the spindle. The nucleus then 

 divides by constriction. By repeated divisions of this kind, eight nuclei 

 are ultimately formed (Fig. 110, 4-7). The cytoplasm now becomes 

 separated into an outer clear alveolar layer and a central granular portion 

 which contains the nuclei, and this is followed by the formation of a cyst 

 wall. The cyst has a diameter of 30 to 50 .microns. After encystment, 

 a second period of nuclear multiplication occurs, with the result that as 

 many as sixty nuclei may be formed. The number of nuclei varies con- 

 siderably (Fig. 110, 7-9). The cysts at this stage escape from the 

 intestine and are taken up by other cockroaches. 



In the crop the cyst wall becomes thin, and the centrally arranged 

 nuclei now take up a position at the periphery. The cyst then passes 

 into the mid-gut, where it ruptures and liberates the multinucleate cyto- 

 plasmic body (Fig. 110, 10). A process of budding then occurs, by which 

 small uninucleate amoebse are separated. These buds are supposed to 

 be gametes which unite in pairs, giving rise to zygotes, which gradually 

 increase in size and grow into the free-living adult forms (Fig. 110, 11-23). 



The cycle of development is essentially the same as that of Entamoeba 

 coli. A phase of multiplication by binary fission in the gut is succeeded 

 by encystment. In the case of E. hlattce, nuclear multiplication commences 

 before encystment actually takes place, and is continued after the cyst 



