698 
MR. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSAE. 
severity of section which the nervous connexions between the nectocalyx and the poly- 
pite would endure without being wholly destroyed ; and, as these connexions are always 
most intimate between the polypite and the marginal bodies or the tentacles, the points 
chosen for irritation were the latter. If the reader will endeavour to imagine all the 
curved sections represented in fig. 7 to be absent, as they are in the left-hand portion 
of fig. 6, he will understand that on irritating the tentacle marked A, the polypite P 
immediately responded. On now introducing the incision marked a a , the polypite still 
continued its response to stimuli applied at A ; but on adding the. cut marked b b, 
such responses ceased. The connexions, however, between C and P were of course 
still intact, and they were not destroyed by introducing the cut c c ; but they were 
destroyed on adding the cut e e. Nevertheless, on now irritating the divided nutrient 
tube in any point of its division k, the polypite still responded ; accordingly the cut e e was 
continued to f, and this had the effect of destroying the connexions between k and P. 
Excitational continuity still subsisted between B and P ; therefore the cut g g was 
introduced : responses still being given, the cut e ef was produced to A, when the 
connexions between P and B were destroyed. Lastly, on irritating D, P responded ; 
but, on introducing the cut i i, responses ceased. 
From this instance it will be seen that, even in the same individual, there are con- 
siderable differences in the degree of tolerance manifested towards section by different 
homologous parts ; but a number of experiments of this kind have satisfied me that 
in Sarsia the loss of excitational continuity between the polypite and bell generally 
supervenes much earlier than does that of contractional continuity between different 
parts of the bell. The preceding sketch, fig. 6, represents the most extreme instance 
Fig. 7. 
of tolerance as regards excitational continuity that I have observed in the case of Sarsia. 
In this instance the polypite continued to respond to stimuli applied at the tentacle 
marked A after the line of junction-tissue marked ab had been reduced to the thick- 
ness of one fortieth of an inch. 
(F) Stimulation of the Convex Surface of the Nectocalyx of Sarsia. — I have this year 
