244 THE GROUSE IN HEALTH AND IN DISEASE 



of the microgamete (about 3 M to 4/* long) it is only with the greatest difficulty that 

 the flagella can be discerned. 



The whole of the micro-gametocyte is not used in the formation of the micro- 

 gametes. When separation of the microgametes from their mother cell occurs, 

 a large amount of the body-substance of the latter remains as a somewhat faint 

 staining residuum, in which the pale staining remains of the karyosome (Fig. 43, cf. 

 Fig. 38) can sometimes be distinguished. The residuum takes no further part in 

 the vital activities of the parasite. 



The microgametes are set free into the lumen of the gut, and proceed to seek 

 out the macrogametes. 



When the macrogamete has attained its maximum development, it often lies in 

 the epithelium, near the outer edge of the tissue, or may even burst through the 

 Fertiiisa- attenuate wall of the host-cell and so reach the margin of the lumen of the 

 gut. The minute but active microgametes (PL xxxvi., Fig. 46) mean- 

 while have broken away from the residual protoplasm of the host-cell, and swum out 

 with rapid lashing movements of their flagella into the gut. Here they are attracted, 

 possibly by some chemiotactic substance, towards the macrogametes. The micro- 

 gametes swarm round the micropyle of the macrogamete (PL xxxvi., Fig. 47 1 ) and 

 several have been seen trying to enter it simultaneously. The nucleus of the 

 macrogamete travels upwards nearer the micropyle, and before long one 

 microgamete effects an entry (Fig. 47 '), appears to bore its way into the female, 

 reach the nucleus, and finally be lost to view. The macrogamete secretes a plug 

 of protoplasm across the micropyle, whereby other microgametes are excluded, and 

 the individuals thus shut out degenerate (Fig. 48). Such is the process of conjuga- 

 tion as seen in the living organism, and the evidence of stained preparations is 

 fully confirmatory of what has just been described. 



Owing to the presence of granules in the macrogamete it is extremely difficult 

 to follow the subsequent stages of fertilisation. Occasionally there are indications- 

 of a fertilisation spindle (Figs. 50, 51), but the nature of the material frequently 

 precluded observation of the same. 



The term " fertilisation spindle " is not exactly a happy one, for the object of 

 that structure is the intimate intermingling of the chromatin of the uniting 

 gametes. 



After the microgamete has reached the nucleus of the macrogamete, fusion 



1 See also PI. xxxvm., Fig. 3, p. 252. 



