1877.] 



Locomotor System of Medusae. 



481 



brium of unusual proportional size. I have given to this animal the specific 

 name of " indicans" because of a highly interesting and important peculiarity 

 of function that is manifested by its manubrium. This function consists 

 in the organ localizing, with the utmost precision, any point of irritation 

 which is situated in the bell. For instance, if any point in the irritable 

 surface of the bell be pricked with a needle, the massive manubrium moves 

 over towards that point, and applies its tapered extremity to the exact 

 spot where the prick has been inflicted. Now this apparent reflex action 

 is independent of the only ganglia that can be shown to occur in 

 the organism, — i. e. the pointing action of the manubrium is not at all inter- 

 fered with by removing the margin of the bell. Accordingly I removed 

 the manubrium at its base, and found that by now irritating any part of 

 its own substance, the apex endeavoured to curve down towards the 

 seat of irritation. Similarly, if only a portion of the manubrium were 

 removed, the pointing action of that portion resembled the pointing 

 action of the entire organ, while the stump that remained in situ would 

 continue to move over as far as it could towards any point of irritation 

 situated in the bell. Hence there can be no doubt that every part of the 

 manubrium is independently endowed with the capacity of localizing a seat 

 of irritation either in its own substance or in that of the bell. And 

 in this we have a very remarkable fact ; for the localizing function 

 which is so very efficiently performed by the manubrium of this Medusa, 

 and which if any thiug resembling it occurred in the higher animals 

 would certainly have definite ganglionic centres for its structural cor- 

 relative, is here shared equally by every part of the exceedingly tenuous 

 contractile tissue that forms the outer surface of the organ. We have 

 thus in this case a general diffusion of ganglionic function, which is 

 coextensive with the contractile tissues of the organ. 



The unerring precision with which the manubrium indicates a seat of 

 irritation in the bell may be completely destroyed by introducing a 

 short cut between the base of the manubrium and the seat of irritation 

 in the bell. The afferent connexions, therefore, on which this locahzing 

 function depends are thus shown to be exclusively, or almost exclu- 

 sively, radial. But although under these conditions the manubrium is no 

 longer able to localize the seat of irritation, it nevertheless continues able 

 to perceive, so to speak, that irritation is being applied somewhere ; for 

 every time the irritation is applied, the manubrium actively dodges about 

 from one part of the bell to another, applying its extremity now at 

 this place and now at that one, as if searching in vain for the offending 

 body. This fact shows that after physiological harmony of a higher 

 order has been destroyed, physiological harmony of a lower order never- 

 theless persists ; or, to state the case in other words, the fact shows that 

 after severance of the radial connexions between the bell and the manu- 

 brium by which the localizing function of the latter is rendered possible, 

 other connexions between these organs remain which are in nowise 



2m2 



