179 
Cytology of Polyphagus Euglenae. 
more. When all the protoplasm and oil-drops have passed into the 
sporangium it is cut off from the parent cell by a transverse partition which 
begins to form at the periphery and gradually extends all across between 
the cells. 
In the germination of the zygote, the outer spiny wall bursts and 
a spherical protrusion of the inner membrane projects through it and 
develops in the same way as just described for the asexual sporangia. 
The protoplasmic contents of the zygote pass into this completely, and the 
sporangium is then cut off by a transverse wall. During all the subsequent 
stages of its development it remains attached to the empty zygote, just as 
the asexual sporangium remains attached to the empty vegetative cell. 
The changes which take place in the contents of a sporangium leading 
to the formation of the zoospores were followed out in several instances by 
continuous observation under the microscope, both in the asexual and in 
the sexual sporangia. These are the same in all essential details in both 
cases, and as Nowakowski has given an account, although not a very com- 
plete one, of the formation of zoospores in the asexual sporangia, I will 
confine myself mainly to a description of the changes which take place in 
the sexual sporangium (see p. 186). 
Cysts. 
These are spherical cells, resembling the smooth-walled zygotes in 
appearance, containing each a single nucleus. They differ from the 
zygotes, however, in the presence of well-developed absorbing filaments 
and in the simpler structure of their membrane. In agreement with 
Dangeard (’ 00 ), I find that the cysts are simply ordinary vegetative cells 
which become surrounded by a thick membrane and enter on a resting 
stage. 
The formation of cysts takes place very readily when the parasite is 
abundant and the supply of Euglenae limited. The cysts are then 
developed in large numbers and often crowded together. Each cyst con- 
tains a single nucleus surrounded by chromidia. The cysts germinate 
easily when placed in fresh cultures of Euglenae, and produce zoosporangia 
similar to those produced by the ordinary vegetative cells, but usually 
much smaller. 
Formation of Zygotes. 
The zygote is formed by the fusion of two ordinary vegetative cells, 
which, instead of producing zoosporangia, become transforme^into gametes. 
The gametes are usually different in size, the smaller one functioning as the 
male, the larger one as the female (Figs. 1-5). Nowakowski observed (’ 76 ) 
two different methods of zygote formation, resulting in the one case in the 
production of a smooth-walled zygote, and in the other of a zygote with 
