i6o 



THE SPOROZOA 



Fio. C. 



in which the two nuclei also 

 fuse, the grains of chromatin 

 being intermingled, but re- 

 taining their distinctness 

 (Fig. 6, b, *^). 



Each sporoblast now 

 becomes a spore in the fol- 

 lowing way. The sporo- 

 blast becomes of oval form 

 and secretes on its surface 

 a tough membrane or sporo- 

 cyst, of a substance resem- 

 bling chitin (Fig. 6, c, Fig. 

 7, A, B). Within the 

 sporocyst the nucleus of 

 the sporoblast, or, as it 

 may now be termed, the 

 sporoplasm, divides into two, 

 then into four, and finally 

 into eight nuclei, by three 

 successive amitotic divi- 

 sions. The eight nuclei 

 take up an equatorial posi- 

 tion, and round each one 

 some of the protoplasm of 

 the spore becomes aggre- 

 gated, and segmented oft' as 

 a minute sickle-shaped germ 

 (Fig. 7, G) termed a spwozoite 



FIQ. 6. 



Formation of gametes (primary sporo 

 blasts) and their conjugation in Mono- 

 cystis, seen in sections, a, portion of 

 a section through a sporont showing 

 the gametes (g) formed at the periphery 

 of the body round the residual proto- 

 plasm (r.p). Occasionally a gamete (g 1 ) 

 may be formed deep in the residual 

 protoplasm, which contains also re- 

 sidual nuclei (r.n). b, the gametes 

 havo fused in pairs to form zygotes, 

 in all of which the fusion of the cyto- 

 plasm is complete, but the nuclei are 

 either still separate Or 1 ) or beginning 

 to unite (r2) or completely fused (r3). 

 The residual protoplasm (r.)>) is break- 

 ing up into separate masses, in some 

 of which degenerating residual nuclei 

 (T.JI) are to be found; n/, cyst -en- 

 velope, o, the zygotes (definitive spm-o- 

 blasts)have begun to secrete sporooysts 

 (./>.<), within which the sporophism 

 (s;>.jp) is becoming contracted ; a lew 

 sporoblasts degenerate (*;/.W). Other 

 letters as before. (After Cuenot.) 

 x 1180. 



