212 



THE SPOROZOA 



in its own substance or laying up any kind of reserve nutriment. It 

 grows rapidly, becoming in twenty-four hours a full-sized, spherical 

 trophozoite. Most remarkable are the changes which take place in 

 the nucleus during the growth of the trophozoite. Larger frag- 

 ments of the chromatin, which was at first scattered evenly in the 

 nuclear framework, collect gradually towards the centre of the 

 nucleus, where they soon appear imbedded in a diffuse, feebly- 

 refractile substance, apparently allied to plastin in nature (Fig. 50, 

 b). The pieces of chromatin fuse with the plastin matrix to form 

 a solid spherical body, homogeneous in appearance, except for a 

 few vacuoles of nuclear sap (Fig. 50, c-e). The body thus formed 

 resembles the nucleolus of Metazoan cells in its appearance and 

 relations, but differs in containing chromatin. It has therefore 

 received the distinctive name of karyosome. The karyosome lies 



Fio. 50. 



Development of a sporozoite into a schizont, showing the formation of the karyosome, in 

 Coccidium schubergi, Schaud. (par. Lithobius forflcatus). After Schaudinn f51J. a, sporozoite 

 with a granular chromatic nucleus (n.sp.z) but no karyosome. 6, larger granules of chromatin 

 appear towards the centre of the nucleus, c, the larger granules become more concentrated. 

 d, they become united by a ground - substance into a central corpuscle or karyosome. e, 

 schizont, with a large nucleus (n.szt) containing the karyosome (ky). 



towards the centre of the nucleus, or slightly excentrically. The 

 rest of the nuclear framework retains its finely meshed condition, 

 and lodges very minute chromatin -granules. The karyosome is 

 retained through all the stages of schizogony, and its presence is 

 absolutely distinctive of the schizogonous generations, but of them 

 alone. 



When the trophozoite is full-grown and has exhausted the host- 

 cell, it proceeds to reproduce itself by schizogony (Fig. 51, 1-IV), and 

 is hence termed a schizont. The schizogony goes on within the host- 

 cell, the withered remains of which form an envelope to the schizont, 

 no cyst or protective membrane being formed by the parasite itself. 

 The schizonts are distinguished by their coarsely alveolar or vacuo- 

 lated protoplasm containing very few granular enclosures, if any. 

 The nucleus of each schizont divides to form a number of daughter 

 nuclei, which travel to the periphery and are scattered at more or 

 less regular intervals at the surface of the cell-body. The proto- 

 plasm adjacent to each nucleus then commences to grow out and 



