38 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



graph on the nervous system of the Medusas (78) that the Acraspeda 

 show a much lower nervous organization than the Craspedota. 



The system naturally groups itself under three heads, the nerve 

 ring, the sensory clubs, and the motor plexus of fibres and ganglia that 

 underlies the epithelium of the subumbrella. The general relations of 

 the nerve ring and of the sensory clubs have been given before in the 

 description of Charybdea Xaymacana, so that we may pass at once to the 

 consideration of the finer details of the nervous tissues. 



In the structure of the nerve ring I have found myself unable to 

 corne to the same results as those given by Glaus, who so far as I know 

 is the only one that has studied the nerve with special reference to its 

 histology. Our difference amounts to this, that he finds two distinct 

 types of cells in the epithelium of the nerve, sensory and supporting, 

 which would make it a receiving as well as transmitting organ, while I 

 have not been able to demonstrate satisfactorily the sensory cells, and, 

 therefore, so far as my own observation is concerned, I am disposed to 

 attribute to the nerve simply the function of conducting impulses. I do 

 not know just how much weight to assign to my inability to find 

 evidence in my sections of the sensory type of cells. Eimer (mentioned by 

 Hesse, '95, p. 420), the Hertwigs (78) and Glaus (78) have independently dis- 

 covered the two types in one medusa or another, and the Hertwigs, at least, 

 have demonstrated them by macerated preparations. So far as Charybdea 

 is concerned, however, Glaus had only preserved material and had to rely 

 upon sections, as have I, since the material which I had preserved with 

 especial reference to maceration did not turn out well. The results that 

 we get from sections vary enough for me to believe that Glaus inter- 

 preted his sections very much by analogy with other forms as indeed, 

 is suggested by his own words (78, p. 22) : " Da es mir nicht gegliickt ist 

 die durch die langere Conservirung in Weingeist fest vereinigten 

 Elemente zu isoliren, habe ich das muthmassliche Verhaltniss beider 

 Elemente nach Analogie der mir fur die Acalephen bekanut gewordenen 

 Verhaltnisse, welche 0. und R. Hertwig so schon auch am Nervenring 

 der Carmarina zur Darstellung gebracht haben, zu erganzeii versucht." 

 There can be no doubt of our having the same structures to deal with, 

 for C. Xaymacana is so much like C. marsupialis as to be perhaps more 

 worthy of being called a variety of the latter than a distinct species. 



The structure of the nerve as I conceive it is given in Figs. 47 and 

 48. The former represents a cross-section, and shows, as others have 

 pointed out, that the layer of circular muscle fibres (cm) is interrupted by 



