SECTION OF COVERED-EYED MEDUSiE. 97 



In conclusion, I may mention an interesting fact 

 which is probably connected with the summation 

 of stimuli before explained. When a contractile 

 strip is allowed to rest for a minute or more, and 

 when a wave is then made to traverse it, careful 

 observation will show that the passage of the first 

 wave is slower than that of its successor, provided 

 the latter follows the former after not too great an 

 interval of time. The difference, however, is exceed- 

 ingly slight, so that to render it apparent at all the 

 longest possible strips must be used, and even then 

 the experimenter may fail to detect the difference, 

 unless he has been accustomed to signalling, by 

 which method all these observations on rate have 

 to be made. 



StiinvJiis-iuaves. 



The rate of transmission of tentacular waves 

 is only one-half that of contraction- waves, viz. 

 nine inches a second. This fact appeared to me 

 very remarkable in view of the consideration that 

 the tentacular wave is the optical expression of a 

 stimulus-wave, and that there can be no conceivable 

 use in a stimulus- wave being able to pass through 

 contractile tissue independently of a contraction- 

 wave, unless the former is able to travel more 

 rapidly than the latter ; for the only conceivable use 

 of the stimulus-wave is to establish physiological 

 harmony between different parts of the organism, 

 and if this wave cannot travel more rapidly than 

 a contraction-wave which starts from the same 

 point, it would clearly fail to perform this function. 



