484 



Mr. G. J. Eomanes on the [Jan. 11, 



Time occupied in passage of contractile 

 Temperature of water. waves through a spiral strip measuring 



28 in. in length and 1| in. in width. 

 sees. 

 26 4 

 32 3 

 42 2f 

 65 2 

 75 If 

 85 Blocked 



Interdigitating cuts interposed in the path of the contractile waves 

 slow the rate of the latter considerably ; and submitting the uncut con- 

 tractile tissue to slight strains has the same effect. So likewise with 

 anaesthetics and a great variety of substances which have no anaesthetic 

 property, such, for instance, as strychnine, fresh water, &c. Lastly, it is 

 observable in a long contractile strip that, after a rest of a minute or 

 more, the first wave that traverses it has a very slightly slower rate than 

 its successor, provided the latter follows the former after not too great an 

 interval of time. This fact is probably connected with the summation of 

 stimuli before explained. 



(B) Stimidus-iuaves. — The rate of transmission of tentacular waves 

 is only one half that of contractile waves, if the stimulation which starts 

 the former is so weak as not also to start the latter. But if the stimulus 

 is strong enough to start both waves, the tentacular wave always keeps 

 an inch or two in advance of the contractile wave. 



V. CoOEDmATIOI^". 



§ 1. Covered-eyed Medusae. — From the fact that in the covered-eyed 

 Medusae the passage of a stimulus-wave is not more rapid than that of a 

 contractile wave, we may be prepared to expect that in these animals the 

 action of the locomotor ganglia is not, in any proper sense of the term, 

 a coordinated action ; and this I find to be the case. IPor, as previously 

 stated, it may usually be observed that one or more of the lithocysts are 

 either temporarily or permanently prepotent over the others — i. e. that 

 contractile waves emanate from the prepotent lithocysts, and then spread 

 rapidly over the swimming-organ. Nevertheless in many cases such 

 prepotency cannot, even with the greatest care, be observed ; but upon 

 every contraction all parts of the swimming-organ seem to contract at 

 the same instant. I am inclined, however, to account for these cases of 

 perfectly S3^nchronous action by supposing that all, or most, of the gan- 

 glia require exactly the same time for their nutrition, and are of exactly 

 equal potency in relation to the resistance (or excitability) of the sur- 

 rounding contractile tissues, and that, therefore, the balance of forces 

 being exactly equal in the case of all, or most, of the gangHa, their rhythm, 

 though perfectly identical, is really independent. 



