294 
ME. G. J. ROMANES ON THE LOCOMOTOE SYSTEM OF MEDUSAE. 
upon staining this small portion of tissue with chloride of gold, I was unable to perceive 
any structural peculiarity that might be supposed to correspond with the functional 
peculiarity which it had previously exhibited. 
( d ) I have now to detail another fact of a very puzzling nature, but one which is 
certainly of great importance in its bearing upon the subject of the present section. 
When the spiral section is performed on Aurelia aurita, and when, as a consequence, 
the contractile waves which traverse the elongating strip become at some point suddenly 
blocked, if the section be stopped at this point it not unfrequently happens that after 
a time the blocking suddenly ceases, the contractile waves again passing from the 
strip into the gonocalyx as freely as they did before the section reached the point at 
which the blocking occurred. The time required for this restoration of physiological 
continuity is very variable, the limits being from a few seconds to an hour or more. 
Usually, however, the time required is from two to four minutes. This process of 
reestablishing the physiological connexions, although rapid, is not so instantaneous as is 
that of their destruction by section. In general it requires the passage of several con- 
tractile waves before the barrier to the passage of succeeding waves is completely thrown 
down. The first wave which effects a passage appears to have nearly all its force expended 
in overcoming the barrier, the residue being only sufficient to cause a very feeble, and 
sometimes almost imperceptible, contraction of the gonocalyx. The next wave, however, 
passes across the barrier with more facility, so that the resulting contraction of the gono- 
calyx is more decided. The third wave, again, causes a still more pronounced contrac- 
tion of the gonocalyx ; and so on with all succeeding waves, until every trace of the 
previous blocking has disappeared. When this is the case it generally happens that 
the strip will again admit of being elongated for a short distance before a blocking of 
the contractile wave again supervenes. Sometimes it will be found that this second 
blockage will also be overcome, and that the strip will then admit of being still further 
elongated without the passage of the waves being obstructed ; and so on occasionally 
for three or four stages. 
The same series of phenomena may be shown in another way. If a contractile strip 
of tolerable length be obtained with the waves passing freely from one end to the other, 
and if a series of parallel and equidistant cuts he made along one side of the strip, in a 
direction at right angles to the length and each cut extending across two thirds of the 
breadth of the strip, the chances are in favour of the contractile waves being wholly 
unaffected by the sections, however numerous these may be. But now, if another series 
of parallel and equidistant cuts of the same length as the first ones, and alternating 
with them, be made along the other side of the contractile strip, the result is, of course, 
a number of interdigitating cuts ; and it is easy to see that by beginning with a few such 
cuts and progressively increasing their number, a point must somewhere be reached at 
which one portion of the strip will become physiologically separated from the rest. The 
amount of such section, however, which contractile strips will sometimes endure is truly 
surprising. I have seen such a strip 20 inches long by 1| inch wide, with ten such cuts 
