310 M. M. Mercatr 
in richly fed animals it is divided into fine granules scattered through 
the nucleus. In one case I found in the rectum of a Ayla viridis 
only six individuals of O. obtrigona all of which were abnormal, 
showing in their degenerating nuclei preliminary phenomena which 
very closely parallel the phenomena accompanying extrusion of the 
vegetative chromatin in normal animals at the time of formation of 
the infection cysts (Figs. 99—118, Pl. XXI). 
Although keeping Opalinae outside the host tends to instigate 
division, life under the unfavorable conditions in the cultures tends 
to so weaken the animals that they generally do not succeed in com- 
pleting the divisions. Division seems normally to be aided by the 
cilia, the swimming movements of the daughter animals tending to 
draw them apart. The cilia beat less vigorously in the animals 
weakened by life in the cultures, and, perhaps chiefly on this account, 
division is rarely completed. In animals which have thus failed 
to complete their division, the nuclei are very often almost completely 
divided so that four daughter nuclei are present, bound together in 
pairs by their connecting threads. Frequently one sees but one of 
the daughter nuclei of the anterior parent nucleus in one cell, the 
other daughter of the anterior nucleus remaining in the other cell 
along with the two daughters of the posterior nucleus, so that this 
cell contains three nuclei, two united to each other by a thread and 
a third united by a thread to the single nucleus in the other cell 
(Fig. 98, Pl. XXI). In nine such instances I have seen the odd 
nucleus in the trinucleated daughter cell either already fused with or 
in the process of fusing with the anterior of the two nuclei which pro- 
perly belong to the cell. This recalls the fusion of nuclei in the zygote. 
In material of O. itestinalis and O. caudata one finds, rarely 
during the fall and early winter, and a little more frequently in 
early spring, individuals with single nuclei of very large size (Figs. 
92, Pl. XX; 96, Pl. XXI). In the character of their mitotic spindle 
and in the distribution of their chromatin these huge nuclei very 
closely resemble the large dividing syncaria in the zygotes in the 
tadpole (cf. Figs. 222, 224, Pl. XXV). The apparently abnormal uni- 
nucleated forms are found in freshly taken material. I have no 
evidence as to the mode of their origin or their relation to normal. 
nuclei. They may possibly be compound nuclei resulting from the 
union of two nuclei, or from the failure of a nucleus to divide. 
The very thick, stocky individuals of O. caudata often seen in 
the spring, have been described’) (Fig. 88, Pl. XX). They may be 
1) page 250. 
