160 CONJUGATION, MATURATION, AND FERTILIZATION 



and among the flagellates as well, this primitive sex differentiation can 

 be traced throughout the entire series, or the "individual" in the sense 

 used in the preceding chapter. In Coccidium, schuhergi (Fig. 74, p. 179) 

 a similar difference is demonstrable for a considerable number of 

 generations, but is not so marked apparently as in adelea. Here 

 fertilization is accomplished by union of a flagellated microgamete or 

 spermatozoid, and a food-stored macrogamete. 



The flagellates, also, present wide variations in anisogamic conjuga- 

 tion, some of them, like Trypanosoma noctuae, being sexually differ- 

 entiated, according to Schaudinn, from the time of the first division of 

 the fertilized cell. In this form of trypanosome, and in other species 

 as well, Schaudinn and different observers have described three dis- 

 tinct types of the organism, females, males, and "indifferent" forms, 

 the latter, under appropriate circumstances, becoming either one or 

 the other sex.^ 



The female trypanosome of Trypanosoma nodum is of relatively 

 large bulk, nearly spherical when mature, and somewhat inactive dur- 

 ing vegetative life. These are the most hardy of all forms of the para- 

 site, because of the reserve store of nutriment which they contain, and 

 these are the forms which, under certain conditions, may undergo 

 parthenogenesis (see p. 163). In order to undergo their full sexual 

 development, the parasites must be taken into the body of a mosquito 

 of the genus Culex, and here the male individuals are transformed into 

 microgametocytes and the females directly into macrogametes. In 

 the male gametocytes the kinetonucleus fuses with the vegetative 

 nucleus and the pigment granules are eliminated. The fused 

 nucleus next divides by a heteropolar mitosis into two nuclei, one 

 large, the other small. The larger nucleus degenerates, while the 

 smaller one divides repeatedly until eight nuclei are present. 

 Each of these divides still again to form a larger vegetative and a 

 smaller kinetonucleus of the future microgamete. The periphery 

 of the cell then draws out into eight projections, each containing 

 one pair of the recently formed nuclei, and these projections are 

 finally pinched off the parent cell as microgametes, each of which, in 

 the meantime, has formed its definite locomotor apparatus of the 

 typical character. The macrogamete, on the other hand, does not 

 form a locomotor apparatus, but after undergoing maturation pro- 

 cesses is sought out and fertilized by one of the microgametes. 



Similar processes have been described by Prowazek, Keysselitz, and 



1 Scliaudinn's observations hax-e been se%-erely criticised and liis conclusions denied by 

 numerous investigators, in particular by Novy and his collaborators; but while these criti- 

 cisms are of undoubted value, the fact remains that Scliaudinn's description of the life history 

 of this parasite of the owl is entirely consistent and the most plausible of all that have been 

 presented in connection with trjqjanosomes, and I give it here as a type of fertilization in 

 trypanosomes in general. 



