FUNDAMENTAL EXPERIMENTS. 35 



eyed Medusci3, I Hn<l it to be uniformly true that 

 removal of the extreme periphery of the animal 

 causes instantaneous, complete, and permanent 

 paralysis of the locomotor system. In the genus 

 Sarsia, ray observati'ms point very decidedly to 

 the conclusion that the principal locomotor centres 

 are the marginal bodies, but that, nevertheless, 

 every microscopical portion of the intertentacular 

 spaces of the margin is likewise endowed with 

 the property of originating locomotor impulses. 



In the covered-eyed division of the Medusie, I find 

 that the principal seat of spontaneity is the 

 margin, but that the latter is not, as in the naked- 

 eyed Medusae, the exclusive seat of spontaneity. 

 Although in the vast majority of cases I have found 

 that excision of the margin impairs or destroys the 

 spontaneity of the animal for a time, I have also 

 found that the paralysis so produced is very seldom 

 of a permanent nature. After a variable period 

 occasional contractions are usually given, or, in 

 some cases, the contractions may be resumed with 

 but little apparent detriment. Considerable differ- 

 ences, however, in these respects are manifested by 

 different species, and also by different individuals 

 of the same species. Hence, in comparing the 

 covered-eyed group as a wdiole with the naked-eyed 

 group as a whole, so far as my observations extend, 

 I should say that the former resembles the latter in 

 that its representatives usually have their main 

 supply of locomotor centres situated in their 

 margins, but that it differs from the latter in that 

 its representatives usually have a greater or less 



