140 THE ANIMAL PARASITES OF MAN 



The merozoites move in a manner similar to that of the sporozoites. The move- 

 ments consist either of slow incurvations with subsequent straightenings, or annular 

 contractions along the entire extent of the body. In addition, there are gliding 

 movements similar to those of many gregarines, and brought about in a like manner 

 by the secretion at the posterior extremity of a gelatinous substance that hardens 

 rapidly. 



The merozoites do not gain the open in the usual way, but are 

 destined to infect still further the same host by actively penetrating 

 into other epithelial cells of the affected organ. Here they continue 

 their growth and may again and again undergo schizogony. In the 

 Infusoria the repeated segmentations finally cease and are renewed 

 only after a conjugation. This is likewise the case with the Coccidia, 

 with the difference that in the latter the two conjugating individuals 

 (gametes) are differently constituted one from the other, whereas in 

 the Infusoria they are almost always similar. 



When the schizogony ceases, the merozoites, that had penetrated 

 the epithelial cells and become trophozoites there, consist of two kinds 

 of differently constituted individuals. One kind possesses a clear 

 cytoplasm (fig. 67, XII), the other an opaque, richly granular cytoplasm 

 (fig. 67, XI), while both possess a vesicular nucleus with a karyosome. 

 In order to continue their development, the more granular individuals 

 must be fertilized, and are therefore termed either female gametes or, 

 on account of their size, macrogametes. The male individuals (micro- 

 gametes) necessary to conjugation, are formed in greater numbers 

 from the less dense microgametocytes or male mother-cells (fig. 67, 

 xnd). They are slender bodies consisting chiefly of nuclear substance, 

 and in most species bear two flagella of unequal length directed back- 

 wards, the place of insertion of which varies according to the species 

 (fig. 67, xiie). 



While the development of the microgametes is rapidly advancing 

 a change occurs in the nucleus of the female parent forms or macro- 

 gametocytes. Parts of the karyosome are extruded (fig. 67, xic), and 

 the nucleus loses at the same time its vesicular form. One macro- 

 gamete results, after nuclear maturation, from one macrogametocyte. 

 By this time the macrogametes are capable of conjugation, and 

 the process takes place within the host, generally, however, outside 

 the affected and degenerated host cells. The microgametes that 

 have now become free from the very large residual body, crowd 

 around the mature macrogametes, which often send out a small 

 prominence ("cone of reception" or fertilization protuberance) for 

 their reception (fig. 67, xin). As soon as a microgamete comes in 

 contact with this and penetrates into the cytoplasm of the macro- 

 gamete, the latter surrounds itself with a membrane which prevents 

 the intrusion of other microgametes. The nucleus of the micro- 



