SOME OBSERVATIONS ON ACINETARIA. 641 
be found lying near the distal end of the macronucleus. In 
section the macronucleus of both the proboscidiform and 
the vermiform individuals is found to possess a distinct 
membrane. In sections of material fixed in both Flemming 
and corrosive acetic the chromatin in the resting nucleus is 
massed in a number of minute granules, an arrangement 
which seems quite different from that in any acinetarian 
I have hitherto examined. 
In well-fed individuals the vacuolar cytoplasm is com- 
pletely blocked with nematocysts, the origin of which will 
be described in the section on feeding. 
In Ophryodendron sertulariz the body is more or 
less disc-shaped, with a marked flattening on its lower 
surface (text-figure 6a). The proboscis takes its origin 
from the lower surface of the animal, and bends upwards 
to end freely in the bunch of tentacles. This is by far the 
most common of all the species of Ophryodendron, but its 
extremely flattened form, coupled with the fact that it usually 
hes closely applied to the theca of a sertularian in such a way 
that only the edge of the animal is presented to the observer, 
render it an exceedingly unsatisfactory object for detailed 
work. 
I have only had one opportunity of examining Ophry o- 
dendron trinacria in a living condition. 
The proboscidiform individual is more cylindrical than the 
proboscidiform individual of Ophryodendron abietinum, 
and the three proboscides arise near the distal end. The 
proboscis does not show any trace of the wrinkling which is 
so characteristic of the contracted proboscis of the other 
species of Ophryodendron, and, in fact, seems to approach 
far more closely a simple apical prolongation bearing tentacles 
such as is found in some species of Acineta. The tentacles 
are rather long, few in number, and distinctly knobbed. 
There is a short hollow stalk, of quite a different structure to 
the solid rod-like stalk which will be described in the section 
on the vermiform individual. 
I have never seen Ophryodendron multicapitatum in 
