132 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



perhaps, still further increased by the result of the 

 following experiments. 



If a covered-eyed Medusa be chosen in which 

 perfectly synchronous action of the ganglia is 

 o))servable, and if a deep radial incision be made 

 between each pair of adjacent ganglia — the incisions 

 beinof thus eiijht in number and carried either from 

 the margin towards the centre or vice versa — it 

 then becomes conspicuous enough that the eight 

 partially divided segments no longer present syn- 

 chronous action ; for now one segment and now 

 another takes the initiative in starting a contraction- 

 wave, which is then propagated to the other 

 seofments. And it is evident that this fact tends to 

 negative the above explanation, for if the discharges 

 of the ganglia are independently simultaneous 

 before section, we might expect them to continue so 

 after section. It must be remembered, however, 

 that the form of section we are considering is a 

 severe one, and that it must therefore not only give 

 rise to general shock, but also greatly interfere with 

 the passage of contraction-waves, and, in general, 

 disturb the delicate conditions on which, according 

 to the suggested explanation, the previous harmony 

 depended. Besides, as we shall subsequently see, 

 for some reason or other segmentation of a Medusa 

 profoundly modifies the rate of its rhythm. In 

 view of these considerations, therefore, the results 

 yielded by such experiments must not be regarded 

 as having any conclusive bearing on the question 

 before us ; and as these or similar objections 

 apply to various other modes of section by which 



