INFUSORIA PARASITIC IN CEPHALOPODA. 191 
The vacuole, which is situated at the posterior end of the 
animal (fig. 9) is contractile. It pulsates at an average 
rate of about once a minute. It is one of the most character- 
istic features of the organism, and it is surprising that its 
contractions have not been remarked before. Most of the 
individuals which I observed contained crystalline bodies in 
their cytoplasm (fig. 9). There is no cystostome. 
Although I succeeded in discovering but a single cuttlefish 
infected with this parasite, I was able to make a considerable 
number of observations upon it. For Opalinopsis survives, 
in carefully made preparations, for several hours after removal 
from its host, and continues to divide actively, thereby pre- 
senting a great contrast to Chromidina. The liver and 
kidneys of the infected Sepia were literally swarming with 
the parasites. 
Very little regarding the nuclear apparatus can be made 
out in the living animal. My description is therefore based 
upon permanent preparations, made with the same precautions 
as those of Chromidina. And here again, I cannot agree 
with Gonder’s interpretation of the appearances presented. 
Feettinger found that “the nuclei . . . sometimes assume 
the form of a network, and all stages are to be found inter- 
mediate between these networks and scattered nuclei—spheri- 
eal or rod-like ”’ (6, p. 373). 
Gonder believed that the changes seen in the nuclear 
apparatus were intimately connected with the division of the 
organism. ‘The cycle of changes is as follows :—“ 1. A com- 
plete resolution and fragmentation of the lumps and particles 
into fine granules... 2. Division of the Infusoria; the 
animals attain their greatest size at the stage of complete 
resolution of the nuclear substances, whereupon they divide. 
3. A reconstitution of the nuclear masses, i.e. the plastin 
collects itself at certain places in the walls of the alveoli, 
together with the granules—so that fragments arise which 
branch out into large bands and slings, out of which the 
nuclear masses—with which we started—are formed” (7, 
p. 254). All these stages are very accurately figured, and it 
