478 



Mr. G. J. Romanes on the 



[Jan. 11, 



activity o£ the latter, any part of tlie irritable surface of the swimming- 

 organ be very gently touched, the resulting contractile wave does not 

 start from the immediate seat of irritation, but from the ganglion which 

 still remains in situ. 



(B) Nervous connexions in Sarsia. — When one of the four tentacles 

 of Sarsia is very gently irritated, it alone contracts. If the irritation be 

 slightly stronger, all the four tentacles, and likewise the manubrium, con- 

 tract. If one of the four tentacles be irritated still more strongly, the 

 bell responds with one or more contractions. In the latter case, if the 

 specimen operated on be non-vigorous or partly ansesthesiated, it may 

 be observed that a short interval elapses betw^een the response of the 

 tentacles and that of the bell. Lastly, the manubrium is much more 

 sensitive to a stimulus applied to a tentacle, or to one of the marginal 

 bodies, than it is to a stimulus applied at any other part of the bell. 



These facts clearly point to the inference that nervous connexions 

 unite the tentacles with one another and also with the manubrium. This 

 inference agrees with the histological observations of Haeckel on Gery- 

 onia, and with those of Schultz on Sarsia, as well as with the results of 

 my own explorations by stimuli already published. But, to place the 

 matter beyond doubt, I tried the effect of introducing a minute radial 

 cut between each pair of adjacent marginal bodies. This operation, as a 

 rule, completely destroyed the physiological connexions between the 

 tentacles. 



But between the tentacles and the manubrium no such definite nervous 

 tracts can be demonstrated by section — that is to say, severance of all 

 the four nutrient tubes, in addition to the marginal incisions just men- 

 tioned, has no effect in destroying the physiological connexions between 

 the tentacles and manubrium. The nervous tracts in this case, therefore, 

 appear to be more or less diffused in the form of a plexus over the sur- 

 face of the bell ; and that this is the case is further indicated by explo- 

 rations wdth graduated stimuli : for during such explorations it may 

 very frequently be observed that the manubrium is more sensitive than the 

 bell to stimuli appHed to the latter ; and in such cases there is evidence 

 of the manubrium being more sensitive to irritation of certain tracts of 

 bell-tissue than to that of other tracts. These excitable tracts, however, 

 are not constant as to their position in different individuals. 



(C) Character of the Excitalle Tissues of Sarsia. — In my former paper I 

 employed the term " physiological continuity " to designate such a con- 

 dition on the part of contractile tissues as admits of an uninterrupted 

 passage along their substance of what I called " contractile waves." I 

 must now introduce another term, viz. " physiological harmony," by 

 which I mean such a condition of contractile tissues as admits of one 

 part responding to stimuli applied at another part, whether or not con- 

 tractile waves are able to pass along the intervening parts. It will be 

 observed that the distinction between these terms has reference to the 



