300 PHYSIOLOGY OF THE INVERTEBRATA. 



Professor B. A. Schafer, F.E.S.,* has shown the presence 

 of " an intricate plexus of cells and fibres overspreading the 

 sub-umbrella tissue " of Aurelia awtita. Dr. Olaus has also 

 described the presence of numerous ganglion-cells in the 

 sub-umbrella of Chrysaora. 



It appears that as far as the nervous system is concerned, 

 the naked-eyed are more highly developed than the covered- 

 eyed MeduscB. 



It is now our intention to briefly allude to the important 

 researches of Dr. G. J. Romanes,! which have been made 

 from the stand-point of experimental physiology. He has 

 studied — (a) the effects of excising the entire margins of the 

 nectocalyces of both the naked-eyed and the covered-eyed 

 Medusm; (h) the efiects of excising certain portions of the 

 margins of the nectocalyces ; (c) the effects upon the manu- 

 brium of excising the margin of a nectocalyx (swimming 

 organ) ; and he has arrived at the following conclusions : — 



" With a single exception to hundreds of observations 

 upon six widely divergent genera of naked-eyed Medusae, I 

 find it to be uniformly true that the removal of the extreme 

 periphery of the animal causes instantaneous, complete, and 

 permanent paralysis of the locomotor system. In the genus 

 Sarsia, my observations point very decidedly to the conclu- 

 sion 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 Medusae, 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 



* Phihfophical Tran tactions, 1878. t Ihid. 1875, p. 279. 



