THE SPOROZOA 213 



project above the surface of the schizont, taking the nucleus with 

 it. Thus are formed a number of club-shaped bodies, each very 

 similar to a sporozoite, but differing from it in certain points of 

 structural detail as well as in origin, and hence distinguished as a 

 merozoite (Figg. 51, IV, and 49, c). The parent schizont, which drops 

 out of the host-cell at this stage, is not converted entirely into mero- 

 zoites, but a certain amount of residual protoplasm is left, destined 

 ultimately to be cast off and to die and break up. 



The schizogony here described takes place in a similar manner in 

 many Coccidia, and has been frequently observed since it was first 

 described by Eimer for the Coccidium falciforme of the mouse in 1870 ; 

 but until recently the connection between the different parts of the life- 

 cycle were not understood, and the schizogonous generations were con- 

 sidered as representing a distinct generic type, to which A. Schneider in 

 1876 gave the name of Eimeria. Hence this portion of the life-history 

 is often termed the Eimerian phase (" Cycle Eimerien "). 



The division of the nucleus of the schizont in the process of schizogony 

 sketched above does not always follow the same method in all Coccidia, 

 not even in the three species inhabiting Lithobius. In Adelea ovata and 

 Coccidium lacazei it takes place by a multiple fragmentation of the nucleus 

 and karyosome, the fragments coming together again at the periphery in 

 patches to form daughter nuclei, each with a central karyosome. But in 

 C. schubergi the nucleus divides by repeated binary fission (Fig. 52, a-e). 

 The karyosome divides first in all cases, and then the chromatin 

 forms two masses round each of the daughter karyosomes, which play a 

 part in the division similar to that performed by the nucleolo-centrosome 

 in Euglena and Paramoeba. The process is one more akin to direct 

 nuclear division than to mitosis, and current descriptions, showing 

 beautiful nuclear spindles, are inaccurate and imaginative (Siedlecki, 

 Schaudinn). The number of merozoitea formed is very variable, and 

 is probably directly related to the nutrition furnished by the host -cell. 

 Usually about thirty or forty, apparently, the number may sink as low as 

 four. Simple binary fission of merozoites or schizonts never occurs, 

 however, since in all cases of schizogony, however much reduced, there is 

 always left a residuary mass of protoplasm on which the merozoites are 

 implanted all round, if numerous, or only on one side, if few. 



The merozoites, at first connected by a stalk with the residual 

 protoplasm of the schizont, soon begin to exhibit active movements 

 and wriggle themselves free. Each merozoite resembles a sporozoite 

 in its movements and general appearance, and differs chiefly in being 

 more club-shaped and in possessing a distinct karyosome. The mero- 

 zoites proceed to seek out and to attack fresh epithelial cells, as did 

 the sporozoites before them, and in a similar way each merozoite 

 grows into a trophozoite which becomes a schizont, and breaks up 

 in its turn into a fresh generation of merozoites. 



In this way schizogony may proceed merrily for many genera- 

 tions, and the numbers of the parasite increase by geometrical 



