COPULATION— C0NJUGATI(3N 75 



are many gametes (Fig. 465); there may be not more than a dozen, as in 

 Schizocystis (Fig. 469), while in the case of Ophnjocystis each gametocyte 

 produces only a single gamete (Fig. 468). 



Amongst the true coccidia or Eimeriidea, the male and female game- 

 tocytes are not associated, but develop in separate cells of the intestine or 

 other organ. The number of gametes produced by each individual may be 

 very unequal in number (Fig. 337). The gametocyte (macrogametocyte) 

 which gives rise to the macrogamete becomes directly transformed into 

 a single macrogamete, while the microgametocyte produces a large number 

 of microgametes. The latter are provided with flagella, and swim away 

 in search of a macrogamete, which is not itself, endowed with the powers 

 of movement. It seems evident that the production of large numbers of 

 microgametes is correlated with the greater uncertainty of the micro- and 

 macro-gametes coming together. In the case of the malarial parasites 

 and allied organisms (Hsemosporidiidea), in which fertilization takes place 

 in the stomach of a blood-sucking insect, the macrogametocyte produces 

 a single macrogamete, while the microgametocyte gives rise to from 

 six to ten microgametes (Fig. 391). In the coccidia belonging to the 

 Adeleidea, the macro- and micro-gametocytes develop in actual contact 

 with one another. The result of this close association is that, though the 

 macrogametocyte gives rise to a single macrogamete, the microgametocyte 

 produces only four microgametes (Fig. 338). In the hsemogregarines of 

 the genus Karyolysus, in which a similar association of the gametocytes 

 occurs, Eeichenow (1921) has shown that the microgametocyte produces 

 only two microgametes (Fig. 457). The marked difference in size betw^een 

 the microgametes and macrogametes in these cases is associated with the 

 conditions under which future development will take place. The macro- 

 gamete is provided with a large amount of cytoplasm heavily loaded with 

 food reserve material to enable it to survive and develop without nourish- 

 ment in the encysted condition. As a result of this provision, as in the case 

 of the ovum, its power of movement has been lost. The male gamete 

 merely functions as a fertilizing agent, for which its nucleus alone is required, 

 and for the fulfilment of which a high degree of motility is an advantage. 



CONJUGATION. — In the type of syngamy which has just been 

 described, the two gametes unite completely and their nuclei fuse. This 

 process is know^n as copulation, to distinguish it from conjugation, which 

 occurs amongst the Euciliata. In typical conjugation two individuals 

 associate, and one of the two nuclei, which each then possesses, passes into 

 the other individual and unites w^ith the nucleus which has remained 

 stationary. As pointed out above, it is possible to regard the two ciliates 

 as each producing two gametes, the small gamete (migratory nucleus) 

 produced by one individual uniting with the large gamete produced by 



