84 Maynarn M. MEITCALF, 
which is the posterior of a pair recently formed by transverse 
division (Fig. 11). Longitudinal division seems, therefore, more 
common than transverse division, as is true for other species of 
Opalina. Opalina has both the Flagellate type of division (longi- 
tudinal) and the Ciliate type (transverse), but the former is much 
more frequent. Probably this is an archaic character. 
One of my specimens shows an interesting condition of the 
nucleus (Figs. 8 and 9). It is an individual which has just come 
from longitudinal division. Its only nucleus is seen to be almost 
divided into two, and one observes that each daughter nucleus is 
already in the somewhat diffuse equatorial plate stage of mitosis 
preparatory to establishing the condition characteristic of fully 
formed resting individuals, i. e. the condition with two nuclei each 
dumbbell-shaped and in a late anaphase of mitosis. The mitotie 
firure resembles closely that seen in O. intestinalis and O. caudata 
at a similar stage of nuclear division. 
The structural conditions in O0. mitotica, as described above, 
suggest discussion of the nuclear conditions in general in the 
Opalinae and in the Oiliata as a whole. Heretofore there have 
been known four species of binucleate Opalinas — saturnalis (LEGER- 
Dusosc), intestinalis (STEIN), caudata (ZELLER) and macronueleata 
(BEZZENBERGER). RArr has just described a fifth — 0. hylarum — 
and a doubtful sixth — O0. binucleata — which I suspeet may prove 
to be but an unusually flattened form of O. macronucleata. I have 
found in Bufo agua, from Jamaica, a very similar form which I am 
still studying. To these four to six binucleate species must now be 
added the very distinet O. mitotica. One quadrinucleate species is 
known — lanceolata (BEZZENBERGER). Fight multinucleate forms 
have been described — dimidiata (Stein), longa (BEZZENBERGER), 
flava (Srorks), lata (BEZZENBERGER), ranarum (EHRENBERG), coracoidea 
(BEZZENBERGER), and obtrigona (STEIN). DOoBELL will soon describe 
a ninth to be named O. vörgula, and I shall soon describe a tenth, 
calling it O. intermedia. I will postpone till a later paper a dis- 
cussion of the remarkable intergradations between the multinucleate 
species. 
Opalina mitotica is especially interesting as showing a transition 
from the binucleate species like öntestinalis and caudata, on the one 
hand, and the quadrinucleate Zanceolata, on the other hand. In 
intestinalis the two nuclei are “resting nuclei”, with their chromatin 
in the typical network condition. ©. mitotica has each of its two 
