ENCYSTMENT 49 



encystment is due to a gradual poisoning of the 

 amoeba causing changes to occur in the ectoplasm, 

 which finally becomes an almost impermeable wall 

 and thus prevents the further absorption of toxic 

 substances. 



In the process of excystation the ectocyst swells 

 up and becomes fainter in outline ; soon a series 

 of minute vacuoles develop in the amoeba just 

 within the endocyst, and protrusions of the con- 

 tained protoplasm are seen to pass through 

 weakened spots in this membrane. In course of 

 time the endocyst gradually disappears, and finally 

 the ectocyst ruptures and the amoeba escapes and 

 leaves the empty cyst wall behind. On two occa- 

 sions we have been able to compare the " dauer " 

 cysts with what we have already termed " conjuga- 

 tion cysts," and the following differences were 

 noted : the latter exhibit neither ectocyst nor 

 endocyst, but merely consist of fluid or semi- 

 fluid contents invested by a cuticle ; indeed, they 

 give one the impression of a minute globular 

 bladder with a faintly yellowish tint. While ex- 

 perimenting with a kinetic jelly containing atropine, 

 cysts having the characters above described were 

 seen to burst, while the " dauer " cysts were un- 

 affected, the conjugation cysts thus appearing to be 

 more permeable and more easily killed. 



Influence of Drought. It should be made clear 

 at once that it is not actual deficiency of moisture 

 which could be supposed to cause the encystment 

 of an amoeba. It is incredible to us that, under any 

 circumstances, the deprivation of water during the 

 drying up, say, of a pond, could be so gradual as 

 to allow the amreba time to encyst. On the other 

 iv 4 



