22O 



THE SPOROZOA 



the microgamete, where its disappointed companions are still to be seen 

 outside the oocyst. The peculiar spindle-like arrangement of the nucleus 

 in the zygote has nothing to do with nuclear division, but is simply a 

 means of mixing intimately the chromatin derived from 'two different 

 sources, and when this is effected the spindle contracts and rounds itself 

 off, the final result being a spherical nucleus, the fusion-product of the two 

 pronuclei. It is usually in the stage with the fertilisation-spindle that 

 the oocyst passes out of the body of the host. 



The nucleus of the zygote proceeds to divide by the direct method 

 (Fig. 51, XI, XII), first into two, then into four nuclei, round each 

 of which the protoplasm segments into four masses, the sporoblasts 

 (archispores, Labbe"). A certain amount of granular protoplasm is 

 left over as a cystal residuum, which occupies the centre of the cyst 



between the four sporoblasts, 

 and is slowly absorbed during 

 the further development. Each 

 sporoblast acquires an oval 

 form, the nucleus being at the 

 centre (Figg. 51, XIII, and 54, 

 a). On either side of the 

 nucleus there is a clear spheri- 

 cal vacuole, one of eight similar 

 vacuoles formed in the zygote 

 containing a viscid substance 

 derived, apparently, from the 

 plastinoid granules before the 

 sporoblasts were segmented off. 

 The sporocyst is now secreted 

 round the sporoblast in two 

 FIQ M coats; the gelatinous epispore 



appears first, then internal to 



Development of the spore of Coccidium schubergi, -rAi. , . 



Schaud. After Schaudinn [51], x 1500. a, sporoblast it the tOUgh refringcnt 

 with spore-membranes, single nucleus, and two 

 vacuoles. 6, the nucleus is dividing, c, two nuclei 



placed at the two poles of the sporoblast, exter- become the Spore. 

 nally to the vacuoles. d, the vacuoles fusing , *\ 



together, e, two sporozoites, arranged ttte-btche, the Sporocyst IS Complete, the 

 and a residual mass of protoplasm containing the 

 vacuole. /, the sporocysts splitting and the two 

 sporozoites escaping, n, nucleus ; vac, vacuole ; 

 en.sp, endospore ; ep.sp, epispore ; $p.z, sporozoite ; 

 ' protoplast -- 



-spi. 



rpsp: 



W1 ,,,i 

 nucleus 



a rt r 

 s HOW 



As soon as 



j- -j 

 Spore divides, 



r.p.sp, residual 



m of the spore. 



, 

 (Fig. 54, b and c). The tWO 



daughter nuclei place them- 



selves at the two opposite poles of the spore, while the two clear 

 spheres come together at the centre and fuse into an oval body (Fig. 

 54, d). The protoplasm of the spore now segments into two sporo- 

 zoites, each with a nucleus, and a central mass of residuary protoplasm 

 containing the above-mentioned oval body, and also a number of 

 plastinoid granules ejected from the sporozoites, which have coarsely 

 alveolar protoplasm free from large granules (Figg. 51, XIV,and 54,*). 



