670 
MR. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSAE. 
influence of the small size of the segment.) But next day the supremacy of the small 
Segment A was not so marked ; for although its rhythm was more regular in the stale 
water than was that of the largest segment, its actual number of contractions in a given 
time was just about equal to that of the largest segment. Again, after transference to 
fresh sea-water, the balance began to fall on the side of the larger segments ; for even 
the quadrant, which in the stale water had ceased its motions altogether, now held a 
middle position between that of the half-segment and the prepotent eighth-part 
segment. On the next day, again, the balance fell decidedly in favour of the larger 
segments, and the weaker eighth-part segment died. Lastly, next day all the smaller 
segments were dead. 
Hence the principal facts to be gathered from these observations are, that as time 
goes on the rhythm of all the segments progressively decreases, and that the decrease 
is more marked in the case of the smaller than in that of the larger segments. This 
lesser endurance of the smaller segments also finds its expression in their earlier death. 
Now as these smaller segments started with a greater proportional amount of ganglionic 
power than the larger segments, their lesser amount of endurance can only, I think, he 
explained by supposing that the process of starvation proceeds at a rate inversely 
proportional to the size of the segment — a supposition which is rendered probable if 
we reflect that the smaller the segment the greater is the proportional area of severed 
nutrient-tubes*. And in this connexion it is interesting to observe that, although the 
endurance of the smaller segments was less than that of the larger as regards the depri- 
vation of nutriment, it was greater than that of the larger segments as regards the 
deprivation of oxygen. This is shown by the greater regularity of the rhythm mani- 
* It may be thought that the greater area of general tissue-mass in the larger segments than in the 
smaller, and not the lesser proportional area of tube-section, is the cause of the larger segments living 
longer than the smaller ones. I am led, however, to reject this hypothesis, because in Sarsia, where seg- 
mentation entails a comparatively small amount of tube-section, there is no constant rule as to the larger 
segments showing more endurance than the smaller ones — the converse case, in fact, being of nearly 
as frequent occurrence. I can only account for this fact by supposing that the endurance of the seg- 
ments of Sarsia is determined by the degree in which the three or four minute open tube-ends become 
accidentally blocked. This supposition is the only one I can think of to account for the astonishing 
contrasts as to endurance that are presented by different segments of the same individual, and, I may 
add, of different individuals when deprived of their margins and afterwards submitted to the same condi- 
tions. Eor instance, a number of equally vigorous specimens had their margins removed, and were then 
suspended in a glass cage attached to a buoy in the sea. Four days afterwards some of the specimens were 
putrid, while others were as fresh as they were when first operated on. Again, as an instance of the experi- 
ments in segmentation of Sarsia, I may quote an experiment in which a score of specimens were divided in all 
sorts of ways, such as leaving the polypite attached to one half, or three marginal bodies in one portion and 
the remaining marginal body in the other portion, &c., &c. Yet, although it was very exceptional to 
find the two portions presenting an equal degree of endurance, no uniform results pointing to the cause of the 
variations could be obtained. In most cases, however, the energy, as distinguished from the endurance, of the 
larger segments was conspicuously greater than that of the smaller. But it is curious that in many cases the 
effects of shoclc appeared to be more marked in the larger than in the smaller segments — the latter, for some 
time after the operation, contracting much more frequently than the former. To show both these effects, one 
