10 



PULSATION OF JELLYFISHES. 



sided, will remain the same as it was before the radiating cuts were 

 made. Moreover, its excited rate, due to being lifted out of water and 

 dropped back, remains the same as it was before the cuts were made. 

 On the other hand, cuts designed to successively reduce the area of the 

 sub-umbrella tissue enervated by a sense-organ (such as are shown in 

 fig. 2, A and B) usually cause the normal rate of pulsation to decline. 

 The excited rates, however, are less influenced by reduction of area, 

 small pieces sometimes pulsating almost as rapidly as large ones, but 

 the duration of the excitement displayed by small pieces is much 

 reduced. For example, in the A series of figure 2 



In the B series the relative areas and rates were as follows : 



The above results are quite similar to those of Romanes uponAurelia, 

 and are opposed to the conclusion of Kimer that severed portions of the 

 disk pulsate at rates approximately proportionate to their respective 

 areas. 



It is interesting to observe that if we stimulate a Medusa into pro- 

 longed and active pulsation at an "excited" rate and then cut out the 

 marginal sense-organs, each sense-organ, together with the piece of 

 tissue attached to it, instantly subsides into a slow rate of pulsation, 

 never faster than the average unexcited rate of the entire Medusa. 

 Moreover, these pieces with sense-organs attached can not immediately 

 be stimulated into a display of. excitement, although after an interval 

 of time they will readily respond and exhibit an excited rate com- 

 mensurable with that of the perfect Medusa. As we have seen, the 

 display of "excitement" is a function of the undiiferentiated tissue of 

 the sub-umbrella, and it appears that the excited rate of the Medusa 

 may be maintained by the influence of the general sub-umbrella tissue 



