252 M. M. Mercatr 
0. zelleri may be but a similar enlarged form of O. dimidiata. 
I have found O. zellert only twice and then in the spring, and the 
thick forms of O. caudata are rather rare, except in the spring at 
a time when many individuals have already become small through 
repeated division. Both Zetier and I have found O. zellert and 
QO. dimidiata together in the same individual host. NERESHEIMER 
describes these two species as from Rana esculenta, but does not 
say if both occur in the same individual host. In no other instance, 
except one very doubtful one in Bombinator, have I ever found two 
species of Opalina in one rectum. BrzzENBERGER describes O. lata 
and O. longa as occurring in Rana limnocharis, but does not say if 
the two species are found together parasitic in the same individual. 
It seems to be very unusual to find two species of Opalina together 
in the same host. The presence of individuals of O. dimzdiata with 
those of O. zelleri in the same host casts some doubt upon the 
status of O. zelleri as an independent species. Until, however, we have 
more evidence of its connection with O. dimidiata, we must, as NERES- 
HEIMER has done, treat it as independent. ZELLER, the discoverer 
of this form, expressed doubt as to its connection with O. dimidiata. 
The chromatin spherules which are formed and dissolved, or 
extruded from the nuclei, during the course of each mitosis, seem 
to be especially connected with nutrition and growth. It is not im- 
possible that careful study of the chromatin spherules in these large 
individuals of O. caudata and O. ranarum and in O. zelleri, might 
throw some light on their: origin, but as yet I have found nothing 
of special import in this direction. JI have not enough preparations 
of nuclei of any of these thick forms, in the right stage of mitosis, 
to allow me to study the point with sufficient care. 
General considerations in connection with the structure 
of Opalina and of the phenomena of mitosis. 
Ectosare and endosare. 
The ectosare and endosare of Opalina are quite sharply distinct, 
both the protoplasmic granules and films and the refractive spherules 
of the two regions staining very differently with many stains. It 
is difficult to suggest to what this may be due. Is the primary 
