48 Journal of Entomology and Zoology 
From the above review it will be evident that we know much 
more about the nervous system of fresh water forms than marine 
ectoprocts, and Gerwerzhagen, 1913, has still further extended our 
accurate knowledge of the nervous system of fresh water forms. 
Most of his information comes from the study of total preparations. 
The general form of the nervous system is shown in Fig. 19A. 
The cerebral ganglion is connected with the two large ganglionic 
cords which have branches to the tentacles by way of the radial 
nerves, each of which has two branches. In the upper part of the 
figure is the oral nerve ring while below is the narrower epistomial 
nerve ring. 
Fig. 19B. shows more detail in the region of the oral nerve 
ring and oesophageal plexus. It shows three bands of commissural 
fibers running across the cerebral ganglion. 
Fig. 19C. shows the general outline of the whole animal with 
the tentacles partly cut away. Besides the general nerves there 
is the nerve plexus of the base which connects with that of other 
members of the colony. 
Fig. 19D. is a side view of part of cerebral ganglion. The 
nerve supply to the epistome shows on the left. 
Fig. 191. shows the nerve supply-to the base of a tentacle; two 
chief branches enter each tentacle, with sensory nerve cells. 
Fig. 19D. shows a diagram of a cross section through the cen- 
ter of the cerebral ganglion. 
In general then the nervous system of Cristella may be sum- 
marized as follows: > 
1. The ganglion is hollow with an extension into the two large 
ganglion cords. 
2. There are two main branches running down each tentacle 
one from each adjoining radial nerve from the ganglinic cord. There 
are also strands from the bipolar sense cells in the epithelium of 
the tentacles. These afferent fibres join the radial nerves on each 
side. 
3. There are two nerve rings, the epistomal or dorsal smaller 
one and the oral or ventral larger one, each with numerous second- 
ary branches. 
4. The sense cells in the tentacles, especially are bipolar. 
Multipolar cells are also found in the nervous system and nerve 
plexus. 
5. There is a ganglion cell network in the wall which con- 
nects one member of the colony with another. This network joins 
