STUDIES ON THE PHYSIOLOGY OF THE iNERVOUS 

 SYSTEM OF CASSIOPEA XAMACHAiNA. 



By Lewis R. Gary. 



INTRODUCTION. 



In this paper are gathered the results of several distinct lines of 

 experimentation, all of which have this in common — that they deal 

 with some phase of the physiology of the nervous system of Cassiopea 

 and represent portions of a general program of research on the nervous 

 system of the lower animals. On account of its ability to live under 

 adverse conditions and to withstand practically any type of operation, 

 Cassiopea is an especially favorable form for experimentation and has 

 been used as a subject for many researches. On regeneration by 

 Stockard, Zeleny, and Goldfarb; for the study of pulsation, rate of 

 nerve-conduction, effect of starvation, etc., by Mayer; on chemical com- 

 position and chemical changes during starvation by Hatai ; on reaction 

 to temperature, permeability, and nerve-conduction by Harvey, and 

 the researches herein recorded by the author. 



In very few types of animals, where the recognizable activities are 

 entirely under the control of nerve-centers, can all these structures be 

 removed without causing death, or at least serious injuries which will 

 render abnormal practically all physiological activities. Among the 

 Scyphomedusae, Cassiopea, in coimnon with many other Rhizostomse, 

 is distinguished for the density of its mesogloea, but it stands preemi- 

 nent as a laboratory marine animal because of the fact that its normal 

 habitat, being in shallow lagoons of relatively stagnant water, fits it 

 especially for the adverse environment encountered under experimental 

 conditions in laboratory aquaria. The sense-organs (nerve-centers), 

 because of their position around the periphery of the disk, can be 

 removed with very little injury to any of the other tissues of the body. 



Since, also, these structures are equally spaced around the circum- 

 ference of the disk, any portion of the body can, by the appropriate 

 operation, be deprived of its normal nerve-supply, while retaining its 

 other relations undisturbed. Then, too, the rapidity with which the 

 centers are replaced by the regeneration of normally functioning new 

 ones permits experimenting on any given area of tissues, first without 

 and later under the influence of nervous impulses. 



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