Cytology of Polyphcigiis Ettglenae. 185 
cells and the two conjugants separate. Then in each individual secondary 
nuclei are formed from the chromidia.’ Somewhat similar phenomena 
occur in Centropyxis aculeata , according to Schaudinn ( } 03), where the nuclei 
degenerate and the sexual nuclei are derived from the chromidia. 
In Pelomyxa , according to Bott (’07), chromidia are extruded by the 
nuclei into the cytoplasm. From these chromidia secondary nuclei arise, 
out of which, by a complex process of extrusion of chromatin and subsequent 
division, the nuclei of the gametes are formed. 
In Polyphagus the nuclear cycle is not so complex, and the primary 
nuclei do not degenerate but remain in close contact with the chromidial 
mass. The chromidia appear to be formed for the purposes of metabolism 
only and gradually disappear, or lose their stainable characteristics, as the 
zygote matures. The two small generative nuclei remain separate until the 
sporangium is formed, when they pass into it along with the other contents of 
the zygote and fuse together to form the primary nucleus of the sporangium. 
The cycle of changes in the chromidia during the development of 
Polyphagus may be summarized as follows : 
The chromidia, as they pass from the zygote into the sexual spor- 
angium, become broken up into invisibly small granules which cause the 
cytoplasm to stain deeply. They are used up in the growth of the spor- 
angium and are reinforced by fresh masses of chromatin extruded from the 
nuclei as they divide. When the zoospores begin to segregate, the diffused 
chromatin gathers round each nucleus and ultimately forfns the deeply 
stainable granular network found around the nucleus in the germinating 
zoospore and the fully developed vegetative cell. When the asexual spor- 
angium is formed, the granular network again breaks up and is disseminated 
through the cytoplasm, to concentrate again round the forming zoospores. 
This process is repeated during successive asexual generations till a zygote 
is formed again. The two nuclei in the zygote are very large and contain 
a great deal of chromatin, which is extruded from them to form two masses 
of granules (chromidia) that subsequently fuse together into a large 
central mass which is visible for some time in the mature zygotes. Just 
at the time the zygotes are about to germinate, this granular mass loses very 
largely its capacity for stains, and on passing into the sporangium, becomes 
diffused in the cytoplasm, and the cycle of changes then repeats itself. 
Germination of the Zygote. 
The two kinds of zygote, the spiny and the smooth-walled forms, 
may be found, as Nowakowski states, in the same culture. The germi- 
nation of the smooth-walled form has been observed by Nowakowski, 
but not the spiny form. He found that germination takes place about 
a month after the formation of the zygote. The large oil-drops become 
reduced in size, or may break up into smaller drops ; the outer wall bursts 
