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Pleistophora gigayitea, Thelohan 
Summary. 
The parasite which I have here described has a life-history con¬ 
taining two distinct stages: a vegetative stage and a sporogonic stage. 
During the vegetative period rnultinucleate individuals divide by 
irregular schizogony producing young uni- or paucinucleate individuals. 
During the sporogonic period, a number of trophozoites unite to form 
an aggregation which becomes encysted. In the encysted individuals 
(the pansporoblasts) there is an increase of nuclear substance and a 
reduction of plasmatic substance. The nuclei become ari'anged in pairs 
and by successive unequal divisions the pansporoblasts produce the 
sporoblasts which contain a pair of nuclei each. During the formation 
of the sporoblasts there is an increase of-protoplasmatic substance. The 
sporoblasts become spores by the thickening of their pelliculae. 
At first the spores contain two nuclei, finally they become mono- 
nucleate. This must be explained by the fusion of the two nuclei. 
This nuclear fusion is probably to be interpreted as a paedogamous 
autogamy (in accordance with the nomenclature of Hartmann, 1909). 
The systematic, position of this parasite. 
According to Minchin’s classification, already mentioned, it is to be 
ranged among the Oligosporogenea because the trophozoite is directly 
converted into a pansporoblast. The number of spores produced by a 
single pansporoblast is not constant, consequently the parasite might be 
considered to belong to the genus Pleistophora, but in P. periplanetae 
(Perrin, 1906), P. longifilis (Schuberg, 1910), etc. we note that the 
spores are formed within the pelliculae of the pansporoblast and not in 
the way described here. Moreover, the structure of the spores of these 
Pleistophorae is very different from that of the parasite of Crenilabrus 
melops ; the aggregation and the united encystment of several indi¬ 
viduals as an introduction to sporogony, are never mentioned in the 
description of the genus Pleistophora. Consequently it is with some 
restriction that I range this parasite among the members of this genus, 
I do so only to avoid the creation of new and perhaps unnecessary 
genera. 
