296 . M. M. Mercaur 
It seems to me that the encystment, which I have often seen 
in dying zygotes and in dying individuals of other sorts, is abnor- 
mal. In material from infected tadpoles, which has been kept too 
long in slide cultures, one sees very many individuals of all sorts 
rapidly change the form of the body, becoming first oval, then 
spheroidal. Following this change of form, they throw off most or 
all of their cilia with many of their basal granules, and extrude 
part of their protoplasm in the manner so characteristic of Opalina 
when under pressure (Figs. 219—221, Pl. XXV). The pellicula 
remains as a very delicate cyst. Within this the body becomes 
very transparent and the nuclei and their contained chromatin be- 
come very clearly visible. Observe especially the granular chromo- 
somes in figures 219 and 220 which show such pseudoencysted in- 
dividuals drawn from ilfe, or rather death (cf. O. caudata, Fig. 275, 
Pl. XXVII). Figs. 210—218, Pl. XXV, show successive conditions 
in copulation and pseudoencystment in one pair of gametes from 
material of O. intestinalis forty-two hours after infection. In this 
case, after complete fusion of the two bodies, the male nucleus broke 
down, entirely disappearing in the cytoplasm of the zygote. The 
female nucleus remained long intact, showing considerable changes 
in the character and arrangement of its contents. Fig. 220 shows 
the condition in another pseudocyst of O. intestinalis, formed after 
the union of a binucleate macrogamete and a microgamete. The 
four granular chromosomes of each female nucleus were very clear. 
The male nucleus had but a single chromatin mass in one side of 
which an elongated body, probably a group of contiguous granules, 
was clearly seen. The excretory vacuole, with its contained excre- 
tory granules in Brownian movement, was also clearly seen. It lies 
uppermost in the figure. Fig. 219, is from a macrogamete of 
O. intestinalis which was found in copulation and was followed through 
a similar series of changes. In this case the nucleus of the macro- 
gamete was in mitosis. Before copulation was complete the animals 
separated again and each formed a pseudocyst in the typical manner. 
There seems no doubt that these instances of encystment and all 
others observed were all abnormal and pathologic. I have never 
found encysted zygotes in material from old infections and I believe 
encystment after copulation does not normally occur. 
I have occasionally seen infection cysts of O. dimidiata, with 
oval nuclei or with one of their nuclei oval while the rest appeared 
spherical (Fig. 286, Pl. XXVII). I doubt if the oval form of the 
nuclei can be taken as evidence that cysts are copulation cysts 
