THE H^MOFLAGELLATES. 181 



and fittingly described by means of the conventional Hsemo- 

 sporidian terminology.^ 



It is most convenient to commence the account of the 

 complicated life-cycle with the zygote or copula, which results 

 from the union of a microgamete with a megagamete in the 

 stomach of the gnat. Even before nuclear fusion is complete, 

 the copula has acquired the vermiform, motile condition, in 

 which it is known as an ookinete (fig. 7). Its hyaline and 

 more refractive anterior end is capable of considerable and 

 rapid changes of shape, now being extended and pointed, 

 now bluntly rounded off. Behind this follows, usually, a 

 region containing one or more lai'ger or smaller clear 

 vacuoles, then a denser cytoplasmic part with the nuclear 

 spindle, and, lastly, the I'ounded posterior end containing 

 pigment and other grains. The movements of the ookinete 

 are identical with those of the corresponding phase in other 

 malarial parasites. The ookinetes next proceed to get rid of 

 unnecessary material, including the pigment-grains and the 

 reduction-nuclei left over in the cytoplasm after fertilisation. 

 These are expelled from the hinder end, enclosed in a portion 

 of the cytoplasm, which is cut off at the same time, and forms 

 a gelatinous investment to the mass (figs. 8 b and e, 9 b, and 

 10 b). 



While this is going on, the complete fusion of the male and 

 female pronuclei into the definitive nucleus {" syukaryon ") 

 is being slowly accomplished. This, however, by no means 

 includes all the nuclear apparatus present, which is of an 

 exceedingly complex character. In T. noctuge the nuclear 

 material is highly differentiated and organised. Not only is 

 there a definite and constant number of chromosomes, but 

 the individuality or '^ separateness " of the principal nuclear 

 constituents, according to their particular function, is very 

 marked. This is revealed in two distinct ways : (a) in the 

 sharp resolution of the nuclear material into trophic and 



' In order to avoid recapitulatory explanation of terms, readers are 

 reminded that a full account of malarial parasites is to be found under the 

 heading " Hsemospoiidia," in Minchin's article (1. c.) on the Sporozoa. 

 VOL. 50, PART 1. NEW SERIES. 13 



