198 M. M. Mercaur 
I desire to thank Geheimrath Prof. Dr. F. E. Scounzn, and 
especially Dr. Max Hartmann for assistance in obtaining numerous 
books. I also wish to thank most cordially the authorities of the 
Smithsonian Institution, through whose kindness I was enabled to 
spend two months at the Zoological Station in Naples. During this 
time I did but little upon Opalina, but had the opportunity to study 
Hoplitophrya, which I was very glad to compare with Opalina. It 
is a pleasure to express my appreciation of the assistance and many 
courtesies received from the Director and Staff of the Zoological 
Station. 
In the spring of 1900 Mr. Ernst Trercumann, at Prof. Bovert’s 
suggestion, began a study of the cytology and reproduction of Opalina 
caudata. The study, however, was never completed. Most of his 
preparations are mislaid and cannot be found, but I have had the 
use of one series of his sections, and more recently Prof. Bovert 
obtained from Mr. TricHMANN his drawings and lent them to me. 
I found in these drawings interesting observations most of which 
my study had already confirmed, but, as Mr. Trrcumann’s results 
were never published, I cannot well refer to them, since, in attempting 
to do so, I would be in danger of falsely interpreting his drawings. 
Material and methods. 
In my study of the cytology of Opalina I have used chiefly the 
binucleated species O. intestinalis and O. caudata, both of which are 
found in the recta of Bombinator pachypus and B. igneus. The nuclei 
in these species are much larger and more satisfactory for study 
than are those of the multinucleated species. Opalina intestinalis 
is especially good, its nuclei being a little larger than those of 
O. caudata. I have also studied O. ranarum, O. obtrigona, O. dimidiata 
and O. zelleri, using all the methods that were applied to the binucleated 
species. 
For the study of the processes of reproduction I have used 
O. intestinalis, O. caudata and O. dimidiata, that is — two binucleated 
and one multinucleated species. 
Infection experiments were made with the cysts of these three 
Opalinas. 
The study of the living animals has given valuable results, 
confirming almost in detail results obtained from the study of 
