74 SYNGAMY IX PROTOZOA 



a gregarine of the earth-worm, Cuenot (1901) described the process of 

 syngamy. Two individuals (gametocytes) encyst together in a common 

 cyst (gametocyst), and each gives rise to a large number of gametes which 

 appear to be completely alike (isogamy). The gametes produced by one 

 individual unite with those produced by the other. The zygotes thus 

 formed become encysted in secondary cysts (oocysts). In his description 

 of syngamy in Monocystis rostrata, another gregarine of the earth-worm, 

 Muslow (1911) also found that there was complete isogamy. 



From this condition of complete isogamy, various transition stages 

 leading to marked anisogamy are known amongst gregarines. Thus, in 

 the case of Lanlcesteria ascidice, Siedlecki (1899), and in the allied form 

 Lankesteria culicis of A'edes argenteus, studied by the writer (1911a), the 

 gametes produced by each gregarine are alike in size, but differ from one 

 another in that those produced by one gregarine have smaller nuclei than 

 those produced by the other (Fig. 465). A gamete with a small nucleus 

 unites with one which has a large one. In the case of Stylorhynchus longi- 

 collis, heger, L. (1904/^) noted that the gametes produced by one gregarine 

 were spherical bodies, while those produced by the other were spindle- 

 shaped structures, each provided with a flagellum. The spindle-shaped 

 motile gametes were actually larger than the spherical ones, so that if 

 the former are to be regarded as the male gametes, this instance affords 

 an exception to the general rule that the male gametes are smaller than 

 the female (Fig. 482). In the case of the gTeganne Pterocephalus nobiJis, 

 Leger, L. and Duboscq (1903a) describe the gametes which are formed from 

 one individual as sniall curved structures (microgametes), and those from 

 the other as large elongate bodies (macrogametes). In this instance there 

 is an approach to the condition which is characteristic of the coccidia. 

 Amongst the coccidia, female gametes or macrogametes are spherical or 

 ovoid bodies filled with food reserve material in the form of globules, while 

 the male gametes or microgametes are minute, elongate, sickle-shaped 

 bodies usually provided with two flagella. The microgametes, which are 

 provided with two flagella, are composed of chromatin covered by a thin 

 layer of cytoplasm, and in many respects resemble the spermatozoa of 

 higher animals (Fig. 337). A similar difference in size exists between 

 the gametes of the pigmented blood parasites of the genera Plasmodium 

 and Hwmoproteus and the non-pigmented Leucocytozoon (Figs. 383 and 391 ). 

 Where a special type of individual, the gametocyte, produces a number 

 of gametes, the actual number produced by each varies considerably in 

 different groups. Amongst the gregarines, where two gametocytes are 

 enclosed in a gametocyst, it is evident that the chance of gametes going 

 astray is reduced to a minimum, so that both gametocytes produce approx- 

 imately the same number of gametes. In the majority of gregarines there 



