[23] 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 segmentation 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 segments 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 conditions. For 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 experiments 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 manubrium attached, to one half, or three marginal bodies in one portion and the remaining marginal body in the other portion, etc. 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 shock 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 experiment may be quoted. A specimen of Sarsia was divided into two parts, of which one was a quadrant.
Immediately after the operation the results were as follows:—
| Portion 1/4. | Portion 3/4. | ||
| Number of pulsations. | Minutes of rest. | Number of pulsations. | Minutes of rest. |
| 20 | 0 | 0 | 5 |
| 4 | 4 | 10 | 2 |
| 15 | 5 | 46 | 1 |
| 6 | 3 | 23 | 2 |
| 49 | 1 | ||
| 45 | 12 | 900 | 1 |
| 117 | 1 | ||
| 1145 | 13 | ||
To show the difference between the endurance of two halves of a bisected specimen of Sarsia, I may quote one experiment which was performed on the same specimen as the one mentioned in the text to show the general relationship between the duration of the pauses and that of swimming bouts. (See last footnote.)
| Immediately after bisection. | |||
| 1/2 A. | 1/2 B. | ||
| Number of pulsations. | Seconds of rest. | Number of pulsations. | Seconds of rest. |
| 56 | 10 | 82 | 180 |
| 150 | 150 | 51 | 20 |
| 68 | 335 | 14 | 60 |
| 130 | 30 | 13 | 50 |
| 46 | 45 | 46 | 45 |
| 2 | 10 | 38 | 45 |
| 99 | 66 | 18 | 45 |
| 103 | 360 | 23 | 60 |
| 12 | 4 | 35 | 130 |
| Pauses now become longer, and swimming bouts shorter. | 105 | 70 | |
| Twenty-four hours after the operation. | |||
| 1/2 A. | 1/2 B. | ||
| Number of pulsations. | Seconds of rest. | Number of pulsations. | Seconds or rest. |
| 2 | 363 | 50 | 20 |
| 12 | 362 | 81 | 25 |
| 4 | 666 | 37 | 101 |
| 25 | 300 | 2400 | 60 |
But although in the case of Sarsia the leaser endurance of the smaller segment than of the larger cannot be regarded as a general rule, it may be so regarded, as already stated, in the case of Aurelia. The following experiment exemplifies this particular rule even more prettily than does the one quoted in the text, from the fact that the segments survived the operation for a greater number of days.
An Aurelia having a regular and well-sustained rhythm of twenty per minute was divided as already described in the text. In five-minute intervals on successive days the average rates of the four segments were as follows:—
| Four hours after the operation. | |||
| Seg. 1/2. | Seg. 1/4. | Seg. 1/8. | Seg. 1/8 A. |
| 100 | 100 | 85 | 90 |
| Next Day. | |||
| 88 | 90 | 64 | 58 |
| Next Day. | |||
| 86 | 82 | 62 | 57 |
| Next Day. | |||
| 59 | 45 | 24 | 20 |
| Next Day. | |||
| 50 | 49 | 20 | 10 |
| Next Day. | |||
| 43 | 33 | 18 | 4 |
| Next Day. | |||
| 39 | 32 | 19 | Dead. |
| Next Day. | |||
| 33 | 7 | Dead. | 0 |
| Next Day. | |||
| 28 | Dead. | 0 | 0 |
Next day, the temperature unfortunately rose sufficiently to cause the death of the single surviving segment, which otherwise would probably have lived for one or two days longer.
[24] This and all the subsequent tracings I obtained by the method already described.