76 THE ANIMAL PARASITES OF MAN 



The reduced nucleus of the macrogamete expands itself on 

 the entry of the microgamete, and becomes a spindle to which 

 the nuclear parts of the microgamete become attached (fig. 30, 

 xiv. and xv.). Thereupon the spindle divides into two daughter 

 nuclei which assume a round shape. The protoplasm at this stage 

 may at once divide, or another segmentation of the daughter 

 nuclei may previously occur. In the former case the two halves 

 divide again, so that finally four nucleated segments, the sporo- 

 blasts, are formed, whereas in the other case the four sporoblasts 

 appear simultaneously. In both cases a residual body of varying 

 size is separated from the protoplasm of the sporont. As a rule, 

 in the meantime, the encysted sporonts have already been dis- 

 charged outwardly, and there, and in the manner described above, 

 form the sporoblasts after a longer or shorter period of incuba- 

 tion. The sporoblasts are originally naked, but they soon secrete 

 a homogeneous membrane in which they become enveloped (fig. 30, 

 xviii.). After the segmentation of the nucleus their contents 

 divides into two sickle-shaped sporozoits, in addition to which there 

 is generally also a residual body (fig. 30, xix.). 



This terminates the development ; the spores are intended for 

 the infection of other hosts. If they attain the intestine of 

 suitable hosts, free or enclosed in the cystic membrane of the 

 sporont, the actions of the intestinal juices cause them to open 

 and permit the sporozoites to escape. The latter move exactly 

 like the merozoites and soon make their way into epithelial cells, 

 where they become schizonts. 



Although our knowledge of the development of the coccidia 

 is but of recent date, yet it already extends to a large number 

 of species, which exhibit varying deviations from the cycle of 

 development described above. The most important deviation is 

 the simplification by the omission of .schizogony, as in Legeria 

 octopiana, which lives in the submucosa of the intestine of cuttle- 

 fish. In these the sporozoites that have invaded the epithelial 

 cells are transformed direct into macrogametes or microgametocytes, 

 which, after the disintegration of the cells of the host, reach 

 the submucosa, where they continue their transformation, copulate 

 and sporulate. Yet in this species auto-infection of the host is 

 not lacking, at all events it has been stated that if the oocyts 

 furnished with numerous spores penetrate from the submucosa into 

 the intestinal lumen, they find themselves in the same condition 

 as if they had been introduced^ per os, that is to say, the spores 

 open themselves and their sporozoites infect other cells. 



