H. B. Fantham 
375 
does not occur in the Selenidiidae, aud it is a point of interest and 
importance. 
The gametocytes of Ophryocystis associate in pairs (Fig. 1, x). 
Nuclear division takes place (Fig. 1 , xi), then nuclear reduction, and the 
two gametes (Fig. 1 , xii, xm) so formed, copulate (Fig. 1 , xiv) and 
produce a zygote, which becomes a single octozoic spore (Fig. 1, xv, 
xvi). The details and significance of these stages will be considered 
later (see pp. 381, 382 and Fig. 4, D). 
Schizocystis. 
The trophozoite of Schizocystis gregarinoides Leger (1900) also 
needs special mention. It is stated to be of large size, some 150/u, long, 
elongate, cylindrical in shape, with a hyaline, anterior portion, the 
whole being non-septate or monocystid. It is multinucleate, and the 
ectoplasm possesses a longitudinally striated cuticle, with a yellowish 
endoplasm containing refringent granules and rod-like bodies. The 
trophozoites are attached by anterior sucker-like ends to depressions in 
the wall of the intestine of the host. The number of nuclei in the 
trophozoite, which is really a schizont, may be as many as sixty, and the 
number increases with the size of the schizont, which starts by being a 
uninucleate, hyaline sporozoite. The schizont divides into a number of 
merozoites, some of which may be from 20/u, to 25/a long, each with 
a single nucleus. The merozoites form uninucleate trophozoites of the 
second generation which are the gametocytes. Association and then 
encystment take place, and conjugation occurs between the gametes. 
In this way many octozoic spores are produced, after the manner 
common to the Gregarines. 
Selenidium. 
As a type of the remaining forms of Schizogregarines with intra¬ 
cellular schizogony, that of Selenidium may be considered. Species 
of Selenidium inhabit tbe digestive tract of various Annelids. One of 
the best known species is Selenidium caulleryi, the trophozoite and 
schizogonic stages of which have been fully described by Brasil (1907). 
This parasite occupies the digestive tract of Protula tubulaHa, and the 
infection is a heavy one. The trophozoite of S. echinatum (Fig. 2) from 
Dodecaceria concharum has also been well described by Caullery and 
Mesnil (1899). 
Parasitology i 
24 
