162 CONJUGATION, MATURATION, AND FERTILIZATION 



autogamy, however, we have to do, probably, with a much more 

 advanced cenogenetic process, and the cells at such periods of 

 activity cannot be regarded as egg cells, since there is no trace of 

 sexual differentiation. 



Not only in different kinds of metazoa, but among some of the pro- 

 tozoa as well, the so-called "females," or egg cells, under certain con- 

 ditions, may develop by parthenogenesis, thus showing a first step in 

 degeneration leading to the method of fertilization by autogamy. Such 

 a possibility seems to have been first suggested by Grassi f'Ol) in con- 

 nection with the organisms of malaria, for he stated "the macrospores 

 (macrogametes) and possibly the microspores (microgametocytes) can 

 increase by parthenogenesis," but the process was first described for 

 the malaria organisms by Schaudinn ('02) in connection with Plas- 

 modnim vivax, the cause of tertian fever. Here the macrogametocytes 

 (but not the microgametocytes) return to the condition of an ordinary 



Fig. 70 



c 











m 



Regression and merozoite formation (parthenogenesis) in Plasmodium -vivax. (After 

 Schaudinn.) A, macrogametocyte in blood with nucleus differentiating into a denser and a 

 lighter part; B, the denser part of the nucleus now divides preparatory to schizogony, C, D, 

 while the paler portion with a part of the original cell degenerates; D, numerous merozoites 

 formed about the divided nucleus. 



schizont after nuclear changes involving loss of a portion of the 

 chromatin. The cell partly divides, one portion containing a faintly 

 staining nucleus, and the majority of the pigment finally is cast off and 

 degenerates. The other portion, containing more intensely staining 

 chromatin, undergoes schizogonv in the manner characteristic of an 

 ordinary blood parasite (Fig. 70). 



A still more remarkable process of parthenogenesis was described 

 by the same author in the case of the flagellate Trypanosoma nociuce 

 (1904), where, as stated above, three kinds of cells were identified as 

 male, female, and indifferent. While the ordinary course is fertili- 

 zation of the female by a much more minute male cell, the macro- 

 gamete, or female, may, under certain conditions, undergo partheno- 

 genesis. The conditions of the environment at such times are such as 

 to bring about marked changes in the organisms. The male cells, or 

 microgametocvtes, are too delicate to withstand the chano-ed conditions 



