THE GREGARINES AND COCCIDIA 335 



unmodified ; in other cases both male and female remain in the 

 undifferentiated condition of the gametid. For an account of the 

 gametes of gregarines, see above (Fig. 79, p. 174). 



Reduction has been described in several cases in the formation of the 

 gametids. In the genus Gregarina the nucleus of the gametid divides twice 

 to form two reduction-nuclei (Leger and Duboscq, 621); Paehler and 

 Schnitzler have also described a reduction- division hi the gametids of Gre- 

 garina ovata. In Monocystis rostrata, on the other hand, the reduction takes 

 place, according to Mulsow (123), in the last nuclear division in the sporont- 

 body, prior to the budding off of the gametids. In this case the ordinary 

 number of chromosomes is eight, as seen in all the divisions of the nuclei ; 

 in the final division the eight chromosomes associate to form four pairs, those 

 of each pair being in close contact, but not fused ; in the mitosis that follows 

 one chromosome of each pair goes to each pole of the spindle, thus reducing 

 the number of chromosomes in each gametid-nucleus from eight to four. 



6. When the gametes are ripe, they copulate in pairs, and 

 probably in every case the gametes of each pair are of distinct 

 parentage. This is certainly the case when the gametes show any 

 trace of sexual differentiation, since those of one sex can be seen 

 to arise from one sporont, and of the other sex from the other. 

 In many cases the two sporonts are separated from one another 

 by a partition dividing the cyst into two chambers, in one of which 

 the male gametes are formed, in the other the female ; when the 

 gametes are ripe, the partition breaks down and pairing of the sexes 

 takes place. 



7. The zygote becomes oval or spindle-shaped, and a membrane 

 is secreted at its surface to form the sporocyst, which becomes 

 an exceedingly tough and impervious envelope, and is generally 

 composed of two layers epispore and endospore. Within the sporo- 

 cyst the nucleus (synkaryon) divides usually three times to form 

 eight nuclei, and then the protoplasm of the sporoblast divides up 

 into as many slender, sickle-shaped sporozoites, leaving over a 

 small quantity of residual protoplasm. The sporozoites are usually 

 arranged longitudinally in the spore, with the residual protoplasm 

 at the centre. The number of sporozoites in the spore is almost 

 invariably eight ; exceptions to this rule are only known amongst 

 the schizogregarines. 



The spores of gregarines differ enormously in different species 

 in form and appearance, and often have the sporocyst prolonged 

 into tails, spines, or processes of various kinds. Various mechanisms 

 may be developed for liberating the spores from the cyst ; for 

 instance, in the genus Gregarina (Clepsydrina) the cyst is provided 

 with sporoducts, and the residual protoplasm derived from the 

 sporonts swells up when the spores are ripe, and forces them out 

 through the sporoducts in long strings. 



8. The ripe spore with its contained sporozoites passes out of 



