PARTHENOGENESIS 89 



tion in the mosquito's stomach, is sometimes able to do so in the human 

 blood-stream without fertilization. The nucleus is described as dividing 

 into two parts, one of which is cast oli with a portion of cytoplasm and 

 degenerates. The remaining nucleus multiplies, and reproduction by 

 schizogony occurs. In this manner it is supposed that the asexual or 

 schizogony cycle is started again, and it was claimed that this afforded 

 an explanation of the occurrence of relapses in malaria. The writer has 

 long held and taught that the parthenogenetic forms depicted by 

 Schaudinn were instances of red blood-corpuscles doubly infected with 

 a gametocyte and a schizont (Plate XII, 19, p. 926). Thomson, J. D. (1917), 

 also came to this conclusion, and showed conclusively that Schaud inn's 

 figures purporting to represent a parthenogenetic process were really 

 instances of doubly infected cells. 



The cases of parthenogenesis recorded by Prowazek (1904) for Herpe- 

 tomonas muscarum and by Gonder (1910a, 19116) for Theileria jmrva have 

 even less evidence to support them than the instance described above. 



The various methods by which syngamy is accomplished amongst the 

 Protozoa may be grouped as follows: 



1. Copulation. — Complete union of two individuals. 



(1) Two individuals having the characters of the ordinary repro- 



ducing forms unite. 

 ((/) The uniting forms are equal in size (isogamy). 

 (h) The uniting forms are unequal in size (anisogamy). 



(2) Two individuals (gametocytes) give rise to a number of smaller 



forms (gametes) which unite in pairs, 

 (a) The gametes produced by the gametocytes are equal in 



size and characters (isogamy). 

 (6) The gametes produced by one individual are unlike 

 those produced by the other (anisogamy). 



(i.) The number of gametes produced by the gameto- 

 cytes are equal, or approximately equal, in 

 number. 



(ii.) One gametocyte (macrogametocyte) gives rise to 

 one large gamete (macrogamete), while the other 

 (microgametocyte) gives rise to a variable 

 number of small motile gametes (microgametes). 



2. Conjugation. — Two individuals (conjugants) associate, their nuclei 

 divide, and exchange of daughter nuclei takes jjlace, after which the 

 conjugants separate. 



(1) The conjugants are equal in size. 



(2) The conjugants are unequal in size, one, a small one (micro- 



conjugant), associating with a large one (macroconjugant). 

 In some cases, after interchange of nuclei the microconjugant 

 degenerates. 



