STRUCTURE, ETC., OF PLEISTOPHORA PERIPLANETH. 627 
production of resting spores. As Stempell remarks, 
Schaudinn’s grouping of the Myxosporidia and Sarcosporidia 
together as a sub-class separate from the rest of the Sporozoa, 
is probably well-grounded, but the difference between the 
two sub-classes must be expressed in other terms than the 
period in the life history at which sporulation occurs. The 
evidence afforded by the disporous Phzenocystes, in which the 
trophozoite produces only one pansporoblast, which gives rise 
to two spores, while the residual protoplasm ultimately dies 
off, and the conversion of the trophozoites of Thelohania 
and Gurleya into a single pansporoblast, support this view. 
Another point of interest in the life-history of Pleisto- 
phora periplanete is afforded by the existence of the 
residuary nuclei,! which, together with the protoplasm of the 
pansporoblast, die off, while sporulation is being effected. 
In the remaining members of the Cryptocystes and all the 
Pheenocystes, with the exception of the Disporea—also “free” 
parasites—no such separation of residuary nuclei occur. In 
the Disporea two residuary nuclei are left behind to die off, 
one for each spore of the pansporoblast. The meaning of 
these residuary nuclei is obscure. At first sight it would 
appear that the residuary nuclei and protoplasm are together 
homologous with that part of the trophozoite of the Disporea 
which remains after the separation off of the pansporoblast, 
but if this is the case, what represents this residuary mass of 
nuclear material and protoplasm in the remainder of the 
Oligosporogenea, including Thelohania miilleri, Gurleya, 
etc., in which the trophozoite is converted bodily into the 
pansporoblast with no residuum ? 
It is significant that in Thelohania miilleri, while the 
spore in its final form possesses two nuclei just like Pleisto- 
phora periplanete, these two nuclei increase to four in 
number while lying in the gut of a new host (Gammarus) 
before germination. Stempell regards this process as one of 
nuclear reduction, preliminary to conjugation with the ame- 
boid contents of another spore. In view of the above fact it 
1 See spore formation, p. 621, 
