148 Mr. Gr. J. Romanes on the [Dec. 16, 



specimens. Further, if the margin be now removed, the paralyzed bell 

 will respond to stimuli applied at any part, just as readily and simul- 

 taneously over its whole extent as it would do were there no system of 

 interdigitating cuts present. 



(b) If the margin of Sarsia be removed in a continuous strip, with the ex- 

 ception of one end left attached in situ, and if the section be then continued 

 in the form of a spiral having two or more turns from the base to the apex 

 of the cone, the contractile waves originating in the free portions of the 

 severed margin pass into the spiral upon reaching its point of origin, 

 and then run round and round the spiral from the base to the apex 

 of the cone. If the marginal strip be now removed altogether, the 

 paralyzed bell will respond to stimuli applied to any part of the spiral. 



(c) If seven lithocysts be removed from the gonocalyx of Aurelia aurita, 

 and if the remaining one be made the point of origin of a spiral section, 

 which is then carried round and round the disk- shaped gonocalyx, the 

 result is a long strip of contractile tissue, the contractile waves always 

 originating in the lithocyst at the end of the strip, and then running along 

 the strip until they deliver themselves into the remainder of the gono- 

 calyx, which thereupon contracts. The length and width of such contrac- 

 tile strips are very important factors in determining whether the waves 

 pass all the way along the strip or become blocked at some point in its 

 length. Nevertheless these are very far from being the only factors, 

 there being immense individual differences in the endurance of the con- 

 tractile tissue under this form of section. Sometimes the waves will 

 become blocked when the strip is only an inch or less in length ; while at 

 other times the waves will pass freely from end to end of a contractile 

 strip which is only an inch wide and a yard long. 



§ 2. How are the impulses transmitted from the locomotor centres of 

 Medusae to the contractile tissues of their swimming-organs ? Have we 

 any evidence of more or less definite lines of discharge being present ? or 

 must we conclude that the contractile tissues are, throughout their extent, 

 of a functionally homogeneous nature ? 



(a) The fact that the contractile tissues endure such severe section 

 without losing their physiological continuity, appears to settle this question 

 in favour of the last-mentioned alternative. Nevertheless there is a 

 weighty body of evidence to be adduced on the other side. In the first 

 place, the extreme variations in their tolerance of spiral section which 

 are manifested by different individuals of the species Aurelia aurita 

 appear to be irreconcilable with the hypothesis of the tissue concerned 

 being functionally homogeneous. But the following invariable fact is 

 still more difficult to reconcile with this hypothesis, viz. at whatever point 

 in a contractile strip that is being progressively elongated by section the con- 

 tractile wave becomes blocked, the blocking is sure to take place completely and 

 exclusively at that point. In view of these facts, therefore, at the present 

 stage of my inquiries, I provisionally accept the hypothesis of more or less 



