262 Vniversitii of California Publications i)i- Zoologij [Vol. 16 



granular in both living and stained material (pi. 20, figs. 63, 66). As 

 stated above, there are neither food nor contractile vacuoles present, 

 though the latter are found during early encystment and during 

 excystment. There are many chroniidia in a newly formed cyst, but 

 only an occasional one during later stages. 



The nucleus of the cyst is from one-fourth to one-third the diameter 

 of the entire cyst. It has two characteristic conditions. One of these 

 is that found in a cyst immediately after encystment and prior to 

 excystment, in which the karyosome is spherical and compact (pi. 21, 

 figs. 79, 83). The other is found in old cysts and in it the chromatin 

 is broken up, but lies within the nuclear membrane (pi. 20, figs. 64-66; 

 pi. 21, fig.s. 84—86). No cyst has ever been found without a nucleus 

 and in which the chromatin is all in the form of chromidia as Brodsky 

 (1910) describes iov Amoeba hyalina Dangeard, and Amdt (1914) for 

 ,4. cJtOHclrophora. 



In the compact condition the karyosome has a diameter from a little 

 more than 0.5 to 0.8 that of the nucleus. It does not take the stain 

 deeply in the recently encysted individuals 



There are various modifications of the broken-up condition to be 

 found in old cysts. There is visually a single rounded mass, though 

 there may be two or sometimes more, which are probably karyosome 

 remnants. It has around it, rather closely connected with it, other 

 chromatin. This condition looks not unlike a .short spireme which has 

 a nucleolus associated with it (pi. 21, fig. 86). The outer chromatin 

 is never in a sphere and is not on the nuclear membrane as is the case 

 with the peripheral chromatin of the trophozoite (pi. 20, figs. 64—66; 

 pi. 21, figs. 84-86). 



The condition seems to be normal and is rather general in cultures 

 five days after encystment. In our culture from which preparations 

 were fixed at intervals during the day every day for seventy days it 

 was found in most of the cysts, not in all, for excystment occurred 

 continuously during that period. The same thing was done in another 

 culture for twenty days and in others for shorter lengths of time with 

 the same results. 



Then to determine the effect of excystment and to find out whether 

 the condition was one which had anything to do with fertilization or 

 not, the amoebas were stimulated to come out of the cysts. A large 

 culture was chosen in which the amoebas had been encysted for fort.y 

 days and in which the chromatin was generally broken up. Numerous 

 cover-.slips taken from this, with fresh medium added, were put in a 



