626 W. S. PERRIN. 
There are several points of interest offered by the above 
scattered details of the life history of Pleistophora peri- 
planetz, both with respect to the Sporozoa in general, and 
the Myxosporidia in particular. In the first place it is seen 
that there are practically two very definite phases in the life 
history, a schizogonous phase, characterised by almost exces- 
sive multiplication with a view to auto-infection, and a sporo- 
gonous phase characterised by the cessation of growth and 
trophic activity and the formation of resting spores. The 
two phases are sharply marked off from one another and cer- 
tain morphological differences are presented by the tropho- 
zoites of the two phases. In this feature, i.e. the sharp 
separation of schizogonous and sporogonous phases from one 
another, Pleistophora periplanetz resembles Thelo- 
hania miilleri, a Myxosporidian belonging to the closely 
allied genus Thelohania, described by Stempell. Stempell 
distinguishes two kinds of trophozoites of Thelohania 
mtilleri—“ meronts,’’ which multiply by a simple form of 
division, and “sporonts,” larger elements, which produce 
resting spores. No such difference of size marks out the 
trophozoites characteristic of the multiplicative and propaga- 
tive phases of Pleistophora periplanetex, but the marked 
difference in behaviour of the two forms of trophozoites, and, 
perhaps, the appearance of the purple nuclei in the tropho- 
zoites about to sporulate, constitute an equally distinctive 
difference. 
The occurrence of sporulation at the end of the schizogonous 
phase by no means agrees with Schaudinn’s division of the 
Sporozoa into T'elosporidia, i.e. Sporozoa in which spore 
- formation occurs at the end of the trophic phase, and 
Neosporidia comprising the Sarcosporidia and Myxosporidia, 
in which spore formation continues during the trophic phase. 
As faras the point in the life history, at which spore formation 
occurs, is concerned, Pleistophora periplanetez is in 
exactly the same position as a Heemosporidian or a Coccidian. 
In each case a trophic phase characterised by vigorous multi- 
plication is succeeded by a resting phase characterised by the 
