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. With regard, therefore, to the original point under consideration, I conclude that, although the size of the segments is doubtless one factor in determining the relative frequency of contraction, there are at least two other factors quite as important, viz. the relative potency of the lithocysts, and the length of time that elapses between performing the operation and observing the rhythm. Hence it is that in my experience I have found but very few examples of Dr. Eimer's rule. _Effects of Other Forms of Mutilation on the Rhythm._ The next point I have to dwell upon is one of some interest. If the manubrium of Aurelia, or of any other covered-eyed Medusa, be suddenly cut off at its base, the swimming motions of the umbrella immediately become accelerated. This acceleration, however, only lasts for a few minutes, when it gradually begins to decline, the rate of the rhythm becoming slower and slower, until finally it comes to rest at a rate considerably less than was previously manifested by the unmutilated animal. If a circular piece be now cut out from the centre of the umbrella, the rhythm of the latter again becomes temporarily quickened; but, as before, gradual slowing next supervenes. This slowing, however, proceeds further than in the last case, so that the rate at which the rhythm next becomes stationary is even less than before. If, now, another circular ring be cut from the central part of the umbrella--_i.e._ if the previously open ring into which this organ had been reduced by the former operation be somewhat narrowed from within--the same effects on the rhythm are again observable; and so on with every repetition of the operation, the rate of the rhythm always being quickened in the first instance, but then gradually slowing down to a point somewhat below the rate it manifested before the previous operation. It will here suffice to quote one experiment among many I have made in this connection:-- An Aurelia manifested a regular and sustained rhythm of 26 Immediately after removal of manubrium, rhythm rose to 36 Rate then gradually fell for a quarter of an hour, and became stationary at 20 Circular incision just including ovaries caused rhythm to rise to 26 After gradual fall during quarter of an hour, rhythm became stationary at 17 Another circular incision carried round midway between the former one and the margin caused rhythm to rise to 24 Rate again gradually declined, and in a quarter of an hour was 12