48 Journal (if 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 

 (igure is the oral nerve ring while below is the narrower epistomial 

 nerve ring. 



Fig. lOR. 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 CristeUa 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. 



;;. 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 



