IV. Coelenterata 



HydrozoA Polyps. The structure of fresh water Hydra has 

 been studied with reference to the nervous system for some time. 

 One of the earlier papers was by Korotneff, '76, who recognized 

 nerve cells. Later work was by T. J. Parker, '80, Rouget, '81, and 

 Schneider, '90. This last author determined a network of ganglion 

 cells to be present. Zoja, '90-'92, finds structures in Hydra which 

 he believes are nervous elements because they take special stains 

 and according to him have connections with the epithelial muscle 

 cells and with nematocysts. These cells are similar to the ganglion 

 cells described and figured by Schneider. 



Citron, '02, in Syncoryne a compound hydroid, finds spindle- 

 shaped sense cells especially in the end knobs of the tentacles. Gang- 

 lion cells with three or four processes are found in various parts of 

 the body while bipolar ganglion cells are found in the coenosarc. 



WoM, '03, determined that hydroid polyps have a nervous sys- 

 tem, partly of sense cells, partly of ganglion cells. The processes of 

 the latter are more or less joined. The sense cells are primitive 

 intra-epithelial. There is quite a complex network of fibers and 

 cells on the body and tentacles, quite a concentration also on the 

 manubrium. Long strands of the plexus run the whole length of 

 the polyp. There is a less abundant entodermal plexus. 



Hadzi in '09, used the isolation method with Hydra, also sec- 

 tioning methods. He found a plexus of nerve cells all over the 

 surface of the body and tentacles ; these were chiefly triangular 

 shaped cells. He distinguishes bipolar and tripolar cells as well as 

 some multipolar forms ; the first are sense cells. He shows anasto- 

 moses at various places. The greater part of the system is an ecto- 

 dermic network. He says that it is not appropriate to speak of 

 neurones, for the cells are directly connected by protoplasmic proc- 

 esses, and Hydra is too far from the type in reference to which the 

 neurone concept was established. 



The palm hydroid Conimorplia, which is more favorable than 

 Hydra tor experimentation, has Iseen studied by Torrey '04, Parker, 

 '17, and others. 



The reaction systems of coelenterates are cilia, nettle cells, 

 mucous glands and muscles. In this genus, mucous glands and cilia 

 are not important. Nettle cells are apparently independent of ner- 

 vous control, a condition not true of Hydra if we accept the work 

 of several investigators. 



There are six sets of muscles in Corymorplia; two of these are 

 entodermic, the circular muscle of the stalk and the circular muscle 

 of the proboscis. When anesthetics which control nervous tissues 

 are used, these two muscles remain capable of acting". This proba- 

 blv shows that these muscles are not under control of the nervous 



