SOME OBSERVATIONS ON ACINETARIA. 647 
more resistant ; in early stages the nucleus retains its charac- 
teristic shield-shape and vacuolar appearance, but under 
the influence of the digestive enzyme its structure breaks 
down, and finally the only trace left of it is a number of dots 
of darkly-staining matter lying in small vacuoles dotted 
through the cytoplasm of the animal. (The characteristic 
Tinctin-k6rper of the Acinetaria.) 
There seems to mea strong probability that the so-called 
chromidia of many protozoa may possess a similar origin from 
the remains of the nuclei of their prey, and I believe that a 
really careful study of this process of digestion of a typical 
metazoan nucleus in the cell-body of a protozoan might have 
a salutary influence on some of the extreme upholders of the 
chromidial hypothesis. 
The nematocysts which remain after the nematoblast itself 
has been completely digested can readily be seen in the living 
animals, and can, by crushing the Ophryodendron, be readily 
exploded. In whole preparations stained with carmine and 
picric acid, and in sections stained with hematoxylin followed 
by eosin, the nematocysts are easily seen. In some cases the 
whole cytoplasm of the Ophryodendron is absolutely blocked 
with them (text-fig. 1), and it is noticeable in such cases that 
the embryonic mass cut off in the formation of the ciliated 
embryos, which will be described later, is relatively far freer 
from nematocysts than the remaining husk of the parent 
individual. 
Whether the adult Ophryodendron has any means of ridding 
itself of these structures must remain an open question, but 
on one occasion [ found a proboscidiform individual which 
had thrown off a mass of cytoplasm containing an enormous 
number of nematocysts which had exploded on contact with 
water. ‘This individual seemed perfectly healthy next morn- 
ing, so that it is possible that the process is a normal one. 
This is the only occasion on which I have found a free Ophryo- 
dendron with exploded nematocysts. 
It is thus clear that the nematocysts of Ophryodendron 
are derived from its host, and this explains the fact that 
