Opalina. 281 
It is interesting to note that at least some of the individuals 
which pass unencysted through the alimentary canal of the tadpole 
to the rectum’) form and extrude chromatin spheres but not quite 
in the normal manner. I have not observed that they encyst if liv- 
ing in the natural species of tadpole. I have, however, had such 
individuals of O. intestinalis and O. caudata encyst in the recta of 
large tadpoles of Rana esculenta four days after the infection was 
secured, and have successfully infected tadpoles of Bufo vulgaris 
with these cysts from the Rana esculenta tadpoles. In two series 
of sections of the rectum of an tadpole of Bombinator pachypus in- 
fected six days with O. intestinalis, I find numerous large individuals 
with eight chromosomes, and numerous smaller forms with four 
chromosomes, extruding their chromatin. Perhaps in the rectum of 
the frog extrusion of the chromatin may occur either before or 
after the reduction in the number of the chromosomes, though usu- 
ally, if not always, under normal conditions the extrusion occurs 
after the number of chromosomes has been reduced. 
Encystment. 
The number of nuclei in the cysts varies with the species and 
within the same species. In one series of preparations of O. ranarwm 
out of 146 cysts tabulated 1 had no nucleus (abnormal), 25 had 
1 nucleus of the ordinary size, 70 had 2 nuclei, 32 had 3 nuclei, 
16 had 4 nuclei, 1 had 5 nuclei and 1 had 6 nuclei. According to 
NERESHEIMER (1907) three to five nuclei are most frequent. Six to 
twelve or more nuclei in the cysts are described by ZELLER, TOnNIGES 
(1899), LozwrentHaL and NeREsHEmMER (1906 and 1907), though these 
larger numbers are infrequent. In O. obtrigona (ZELLER) and O. dimi- 
diata (ZELLER, NERESHEIMER, METCALF 1907 a) conditions are the same 
(Figs. 285—288, Pl XXVIII). In the binucleated species O. saturnalis 
(Lecer & Dusosca), O. intestinalis (ZELLER, Mrercaur) and O. caudata 
(ZeLLER, METCALF) the cysts have generally one nucleus (0. intestinalis, 
Figs. 130—136, 140—143, Pl. XXII; 236, Pl. XXV; O. caudata, 
Figs. 137—139, Pl. XXII; 252, 253, Pl. XX VI) though I have often 
found two nuclei in the cysts of the latter two species (Figs. 254, 
255, Pl. XXVI). Occasionally one finds the binucleated encysted 
animal in the process of division (Fig. 255), though I do not think 
the division can often be completed until the animal emerges from 
") Compare the chapter on infection experiments, page 314. 
