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Cytology of Polyphagus Euglenae. 
Polyphagus is not unlike the common sun animalcule, Actinophrys sol 
Many characteristics are common to both : the uninucleate thallus, the 
radiating pseudopodia connected with, or arising close to, the nucleus, and 
the vacuolate condition of the peripheral cytoplasm. 
In other respects also, as in the peculiar structure of the nucleus and 
the extrusion of chromidia, Polyphagus shows affinity with the Protozoa. 
It is not my purpose here to discuss these relationships, but I cannot 
help feeling that, the more we learn of the general structure and life- 
histories of the Rhizopoda (Sarcodina) and the Chytridiaceae, the more 
apparent it becomes that the attempt to derive the Chytridiaceae £ from 
the higher Phycomycetes by degeneration through parasitism ’ (see 
Atkinson, *09) is an unsatisfactory solution of a difficult problem, and that 
in discussing their phylogeny we must take into account the evidence for 
their possible origin from Protozoan-like ancestors, as Dangeard has 
maintained (’01) , and their development along a progressive line of 
evolution. 
Theoretical Considerations. 
The study of the nuclear cycle of Polyphagus affords clear evidence of 
the dual nature of the nucleus, and perhaps throws some light upon the 
delayed nuclear fusions and the double nuclear fusions observed in the 
sexual reproduction of some of the higher groups of the Fungi. 
That nuclei have both somatic and generative functions is well known, 
and Schaudinn (’03) suggested that these two functions reside in two 
distinct parts of the nucleus and that each cell is therefore in a sense bi- 
nucleate. Goldschmidt (’04, ’05) put this in an extreme form when he 
brought forward the definite hypothesis that every cell is essentially 
binucleate and possesses a somatic nucleus with metabolic functions and 
a propagative nucleus with generative functions. In the Infusoria it has 
long been known that these two elements are differentiated in the cell as 
a macro-nucleus and a micro-nucleus, but in other organisms they are united 
in a single structure which he calls * amphinucleus \ In Polyphagus 
it seems quite clear that the nucleus has this dual structure to the extent 
that the chromidia represent the vegetative or somatic element and the 
small nuclei, left after the extrusion of the chromidia, the generative element. 
This is not, however, sufficient to warrant the conclusion that the chromidia 
owe their existence to the activities of a somatic nucleus which has an 
individuality of its own apart from a generative nucleus. 
The double fusion which takes place in the life-cycle of Poly - 
phagus is clearly bound up with this dual function of the nucleus, the 
chromidial fusion in the zygote promoting vegetative growth, whilst the 
nuclear fusion in the sporangium precedes the formation of the spores. 
Ihe importation of two nuclei into the zygote appears therefore to be 
