376 
The Schizogregarines 
The trophozoite of Selenidium is an elongate, vermiform, uninucleate 
organism (Fig. 2, A), roughly circular in transverse section, about 75 g 
long and 25 /a broad in S. caulleryi. The anterior end is prolonged into 
a partly eversible or retractile epimerite, ectoplasmal in nature and clear 
and hyaline in appearance (Fig. 2, A, ep). The epimerite is lost later in 
the life of the organism. The posterior end is nai’rower than the anterior, 
the general shape being falciform, with a distinct curvature (Fig. 2, A). 
The trophozoite is motile, its movements being chiefly of flexion. 
Fig. 2. Selenidium echinatum, after Caullery and Mesnil (1899). 
A. Free trophozoite, ep = epimerite, n=nucleus, »«// = myonemes. 
B. Two gametocytes in association. 
C. Cysts full of sporoblasts or young sporocysts, from a fresh preparation. 
D. Spherical sporoeyst showing spiny exterior (epispore). 
E. Transverse section of sporoeyst, with tetrazoic sporozoites, spz. 
F. Two free sporozoites. 
The ectoplasm exhibits a series of fine, longitudinal, contractile 
striae, the myonemes (Fig. 2, A, my), which traverse the entire length 
of the body. Often 20 such myonemes are present, but the number 
varies for different species of Selenidium and may be smaller, e.g. four. 
The endoplasm is highly granular; little endoplasm is present in the 
epimerite region and it is less abundant at the posterior end of the body. 
The nucleus is large and in a few species {e.g. S. echinatum ) it is 
nearly spherical in shape (Fig. 2). In most species the nucleus is 
elongate oval, its long diameter being directed transversely with regard 
to the long axis of the animal (Fig. 3, n, vi). The nuclear membrane is 
very slightly marked, and the nucleus is filled with nuclear sap, some¬ 
what granular in character, which surrounds the large laterally placed 
karyosome. 
