The following observations were made on a healthy specimen of Aurelia having all its lithocysts in good condition, but prepotency being well marked in the case of one of them, and also, though in a lesser degree, in the case of another. I divided the animal so as to leave one of these two prepotent lithocysts in each of the eighth-part segments, and the next most powerful lithocysts in the quadrant segment. In the following description, I shall call the two eighth-part segments A and B, the former letter designating the segment containing the most powerful lithocyst. The Aurelia before being divided manifested for several hours a very regular and sustained rhythm of thirty-two per minute. After its division, the various segments contracted at the following rates, in one-minute intervals:-- -----------+------------+------------+--------------+-------------- Time after | | | | operation.|Segment 1/2.|Segment 1/4.|Segment 1/8 A.|Segment 1/8 B. -----------+------------+------------+--------------+-------------- 1/2 hour. | 20 | 25 | 27 | 15 1 " | 20 | 25 | 27 | 15 2 hours.| 29 | 25 | 27 | 16 4 " | 19 | 16 | 27 | 12 -----------+------------+------------+--------------+-------------- Next morning, the water which contained the segments was somewhat foul, and this, as is always the case, gave rise to abnormally long pauses. This effect was much more marked in the case of some of the segments than in that of others. I therefore observed the segments over five-minute intervals, instead of one-minute intervals as on the previous day. The following is a sample of several observations, all yielding the same general result.