THE INTESTINAL PROTOZOA OF FROGS AND 'TOADS. 211 
observing the living animal. After this stage the animal 
completes its division with great suddenness. After remain- 
ing for some time in the state shown in fig. 10 a kind of con- 
striction appears very suddenly in the middle (fig. 11). The 
constriction deepens all of a sudden, and then almost 
disappears again, appearing as though an unseen string were 
suddenly tightened and then loosened around the animal. 
This welling in and out lasts for several seconds, being 
repeated some half-dozen times, and then in a flash the 
creature is snapped in two by the constriction being com- 
pleted, and two little daughter monads are left facing in 
opposite directions (fig. 12). For several seconds they 
remain thus, moving their flagella but feebly. Then they 
become more active by degrees and swim away from one 
another. It is seen that each monad possesses all the 
organelle of the adult, and it is also perfectly plain that the 
rod which united the daughter blepharoplasts has, by dividing 
transversely, furnished each daughter monad with its axostyle. 
The axostyle is thus re-formed by the blepharoplast at each 
division. I will discuss the interesting points connected with 
this later (see p. 225). 
The behaviour of the cytostome is not easy to make out 
during division. Very often, however, it can be quite clearly 
seen that the cytostome passes over into one of the daughter 
individuals (cf. fig. 10), so that the other individual must 
generate a new mouth. This is in agreement with Prowazek’s 
observations on T. lacerte (738). 
Encystment.—After continuing to divide for an unknown 
length of time Trichomastix batrachorum is able to 
encyst. For along time I was quite unable to find any trace — 
of encysting in this animal. Even now I have not.the remotest 
idea what causes encystment. In the ordinary course of events 
the animals, whether liberated in the feeces or removed by 
operation from the host, die sooner or later. And this happens 
no matter how they are treated—whether allowed to dry, 
whether placed in water, whether kept moistened in the 
feces. All experiments to determine the cause of cyst- 
