158 



THE SPOROZOA 



D. T 



dir. 



fl 



FIG. 5. 



Formation of the segmentation- 

 nucleus, and its subsequent division, 

 in sporonts of Monocystis. a, portion 

 of a section through two encysted 

 associated sporonts, separated by 

 their cuticular body-walls (c.w). In 

 the lower half of the section is seen a 

 nucleus in which the karyosomes (ky) 

 are breaking up, while in the nuclear 

 sap near them a number of granules 

 of chromatin have appeared to form 

 the segmentation - nucleus (n.seg). 

 Outside the nuclear membrane a 

 patch of archoplasm (arch) has appeared. In the upper half the archoplasm has divided 

 to form an achromatic spindle (ac.sp), in the middle of which are seen the chromatin granules 

 of the segmentation -nucleus; two karyosomes are also seen, one showing a vacuolated 

 structure. 6, section through one sporont of an associated couple in a cyst, showing the 

 segmentation-nucleus in the diaster stage. The karyokinetic spindle (ac.sp) stretches across 

 the whole body. The chromosomes (chr) form two groups, c, section through a couple of 

 encysted sporonts, showing in the lower one two resting nuclei preparing for division, and the 

 remains of a karyosome in the cytoplasm ; in the upper one two nuclei in the diaster stage, and 

 two karyosomes ; ep, epicyst ; en, endocyst. d, section through one sporont of a couple showing 

 seven resting nuclei (n), one dividing nucleus (?uc), and two karyosomes (ky). (After Cuenot.) 

 a, x 1180 ; b and <l, x 500 ; c, x 790. 



