Opalina. 283 
zusammen und scheiden, indem sie sich dabei schneller oder langsamer 
drehen. eine farblose, glashelle Cyste wm sich ab.” 
The cysts vary considerably in size. They are mostly spherical 
or nearly so, some are oval (Fig. 130, Pl. XXID, and a few some- 
what irregular in form. One frequently sees encysted animals many 
of whose ectosare spherules are at the extreme outer edge of the 
ectosare (Fig. 134, Pl. XXII), and in a few instances, I have seen 
cysts in which, between the cyst wall and the ectosarc, there were 
numerous refractive globules which seemed to be extruded ectosare 
sperules (Fig. 135, Pl. XXII). It is easy to see in some cases a 
mass of granular debris left behind, in the cysts which the animals 
are leaving (Fig. 140, Pl. XXII). Other cysts are left entirely 
empty when the animal hatches, no such debris being found (Figs. 
142, 143, Pl. XXII). It seems as if some individuals, during en- 
cystment, got rid of an excess, through generally not of all, of the 
ectosarc spherules. 
Cysts of O. ranarum stained with Moors & Brert’s lithium- 
iron-haematoxylin often show the presence of endosarc spherules. 
On the other hand many cysts contain no endosarc spherules. In 
minute individuals ready for encystment and in slightly larger forms, 
similar diverse conditions are seen. In the binucleated species and 
in O. dimidiata most if not all of the animals hatching from the 
cysts contain endosare spherules. The presence or absence of the 
spherules in O. ranarum is probably dependent on nutrition. 
It happens that none of my sketches of O. intestinalis show 
binucleated cysts, though I have seen many. Fig. 124, Pl. XXII, 
shows a binucleated individual in the process of encystment. 
Before hatching from the cysts the little Opalinae become very 
active, the speed of their revolutions increasing until one becomes 
fairly dizzy as he watches them. Cysts in the duodenum of the 
tadpole may contain these very active animals, indicating that hatch- 
ing may take place soon after ingestion. Much more frequently 
hatching occurs in the posterior part of the intestine or in the 
rectum. The cyst wall weakens at some point and the little Opalina 
squezes through, sometimes slowly, sometimes rapidly, and swims 
off with a very rapid motion quite different from the motion of other 
individuals. The newly hatched individuals have well developed 
cilia, longer in proportion to the size of the body than are the cilia 
of larger forms Figs. 140—144, Pl. XXII). The cysts begin to 
hatch within three hours of the time of their ingestion, pro- 
bably even earlier. 
