22 NERVOUS SYSTEMS AND SENSE ORGANS 



that although the muscle of the jellyfish is capable of direct stimu- 

 lation, it is not so sensitive as the nerve-net. Parker summarizes 

 the susceptibility to stimulation as follows: 1. Marginal bodies 

 most sensitive. 2. Nerve-net. 3. Muscles directly stimulated least 

 sensitive. 



Mayer, 1917, concludes from his experiments with Cassiopea, 

 that nerve conduction is due to a chemical reaction involving the 

 cations of sodium, calcium and potassium. The probable high tem- 

 perature coefficient of ionization of this proteid may account in some 

 measure for the high tention coefficient of the rate of nerve condi- 

 tion, which he finds is two and five-tenths as great as that of the 

 electrical conductivity of the seawater surrounding the nerve. His 

 observations do not support the "local action" theory. The rate of 

 nerve conduction is practically identical whether sea water is diluted 

 with 0.415 molecular mercuric chloride or with distilled water. 



Corry, 1917, working with the same species found that regener- 

 ation takes place more rapidly on the half of the jellyfish in which 

 the sense organs were not removed. When sense organs are i"e- 

 moved and one half stimulated by electricity and the other insulated 

 half not stimulated, regeneration is more rapid on the activated 

 part. The experiments show that the rate of regeneration is but 

 one expression of the general metabolic activity of the animal and 

 as such is subject to the influence of the nerve centers as are many 

 other functional activities. It is concluded as a result of experi- 

 ments that some chemical interchange between sense organs and 

 the surrounding tissue is necessary in order that the activity of 

 these structures shall be maintained at the highest state of efficiency. 



Some sort of trophic influence is exerted in general metabolic 

 activities by the sense-organs. The structure of the nervous system 

 of this form makes it impossible to prove the existence of tropic- 

 nerve fibers as distinct from those of sensory or motor functions. 



In Pelagia, Krasinska finds large and small ganglion cells in 

 association with sense cells. The large ganglion cells are considered 

 to have a motor and the smaller ones a sensory function. There 

 are three methods of connecting the nerve plexus with the epithelial 

 surface. (1) Through peripheral processes of the ganglion cells. 

 (2) Through sense cells. (3) Through free nerve endings. No 

 direct proof of the enervation of the muscle fibers was established. 



The tentacles have large and small ganglion cells, the cells are 

 deep in the muscular folds but in the outer epithelium is a fine 

 nerve-fibrillar area. Similar fiber masses are found in other parts 

 of the body and the nervous system ; these may correspond to a 

 "neuropile." Fibrillae were found especially in the branches of 

 the ganglion cells. 



ACTiNiANS. The reactions of the actinians have attracted at- 



