i95 
Cytology of Polyphagus Euglenae. 
observations on Pyronema , considers that the fusion in the ascus should be 
regarded as the completion of the sexual fusion, for he maintains that, 
although there is a normal cell fusion of antheridium and ascogonium, there 
is no nuclear fusion in the ascogonium. He suggests that the male and 
female nuclei simply become paired in the ascogonium and subsequently 
divide by conjugate division in the ascogenous hyphae and fuse ultimately 
in the ascus. This would bring the Ascomycetes into line with Polyphagus 
and the Uredineae, but the very definite observations of Harper, followed 
by Blackman, Frazer, and others, that in some forms there is a nuclear 
fusion in the ascogonium as well as a subsequent fusion in the ascus, 
preclude our acceptance of the easy solution of the problem offered by 
Claussen, and we must look for it in another direction. 
If we consider that in the nuclei of the Ascomycetes, as in other 
forms, we have the two elements, the generative and the vegetative, is it not 
possible to conceive the first fusion of the nuclei in the ascogonium as 
a purely vegetative fusion, and the second fusion in the ascus as the 
generative fusion ? In other words, may not the nuclear fusion in the 
sexual apparatus and the nuclear fusion in the ascus be simply regarded as 
the vegetative and generative phases of a single sexual act which have 
become separated owing to the interpolation of a series of vegetative 
divisions between the formation of the ascogonium and the production of the 
ascospores ? 
This conjecture seems the more reasonable when we remember that in 
so pronounced a sexuality as that of Polyphagus the nuclei do not fuse in 
the zygote, but only those portions of the chromatin extruded from them 
which are obviously bound up with vegetative development. And it is further 
supported by the trend in the direction of non-sexual fusion shown by the 
Ascomycetes in general, as indicated by the total disappearance of cell 
fusion in many forms and its reduction to mere pairing in others, but leaving 
in all cases the generative fusion of nuclei in the ascus. 
Summary. 
1. Polyphagus Euglenae is one of the few Chytridiaceae in which there 
is pronounced sexuality. Reproduction takes place by the production of 
zoospores in sporangia, which may be formed on the ordinary vegetative 
cells, or on cysts, or on the sexually produced zygotes. 
2. The organism is parasitic on Euglena viridis. The thallus is 
unicellular and uninucleate, and is provided with delicate pseudopodia 
which penetrate the cells of the Euglenae and bring about complete 
disintegration of their contents. A single thallus may be in contact with 
as many as fifty Euglenae. 
3. The zoospore possesses a single flagellum, at the base of which 
is a yellow oil-drop in close contact with the nucleus. The nucleus is 
