3o6 THE POPULAR SCIENCE MONTHLY. 



pulsations of the bell instantly and forever ceased. On the other 

 hand, the severed margin continued its pulsations with vigor and per- 

 tinacity, notwithstanding its severance from the main organism. For 

 hours and even for days after its removal the severed margin would 

 continue its rhythmical contractions ; so that the contrast between the 

 death-like quiescence of the mutilated bell and the active movements of 

 the thread-like portion which had just been removed from its margin 

 was a contrast as striking as it is possible to conceive. 



I may here add that, although excision of the margin of the bell thus 

 completely destroys the spontaneity of the bell, it does not at all dimin- 

 ish the excitability of tl)e bell ; so that, although the mushroom-shaped 

 mass will never move of its own accord after having been thus muti- 

 lated, it will give any number of locomotor contractions in response to 

 an equal number of artificial stimulations, just in the same way as a 

 frog with its head (nerve-centres of spontaneity) removed will give any 

 number of hops in response to successive stimulations. 



These experiments, therefore, prove conclusively that, in the extreme 

 marginal rim of all the numerous species of Medusae which I examined, 

 there is situated an intensely localized system of nervous centres, to 

 the functional activity of which the rhythmical contractions of the 

 swimming-bell are exclusively due. And as the Medusm are thus the 

 lowest animals in which a nervous system has yet been or probably 

 ever will be discovered, we have in them the animals upon which we 

 may experiment with the best hope of being able to elucidate all ques- 

 tions concerning the origin and endowments of primitive nervous tis- 

 sues. I may here add that these experiments were independently made 

 by Dr. Eimer, of Wiirzburg. 



After I had made the observation which I have described, it seemed 

 to me desirable to follow it up with a number of other physiological, as 

 distinguished from histological, researches. For I was much struck by 

 the certainty and precision of the results which I had obtained by ex- 

 periment, as distinguished from the uncertainty and disagreement of 

 the results which had previously been obtained by the histological 

 methods. Accordingly, I decided, in the first instance, to feel my way 

 in the direction of physiological experiment before beginning that sys- 

 tematic histological research which, sooner or later, it was manifestly 

 imperative to make. Study of function having so far guided the study 

 of structure as to show that it was in the margin of the Medusae, that 

 we must look for the principal if not the exclusive supply of central 

 nervous tissue, it seemed desirable to ascertain hoAV much light a fur- 

 ther study of function might throw on the character and the distribu- 

 tion of the peripheral nervous tissue.' Accordingly, I began my physi- 

 ological work chiefly with the view of guiding my subsequent histo- 



' Although it sounds somewhat paradoxical to speak of the central nervous tissue as 

 distributed ou the periphery of a circular animal, and of the peripheral nervous tissue as 

 occupying all the more centrally situated parts, the paradox is unavoidable. 



