286 LEISURE.TIME STUDIES. 



body be irritated below the cut, as at d, the polypite, in- 

 stead of moving at once to indicate as before the irritated 

 portion, will move in an erratic and undetermined fashion. 

 We have, in plain language, cut the direct connection or 

 line of discharge between the irritated point and the 

 polypite, so that our stimulus has to travel by a nervous 

 loop-line and reaches the polypite after all, it is true, but 

 without affording to that structure direct and definite in- 

 formation concerning the irritated point. The result of 

 the foregoing experiment also serves to impress the idea 

 that habit and use favour the development of special lines 

 of discharge in the jelly-fishes. Tiaropsis is thus able ac- 

 curately to indicate the seat of irritation through certain of 

 its nervous lines only : these being the lines ordinarily used 

 by the animal in the acts of its life. The loop-lines through 

 which the impulses travel after the infliction of our cross-cut 

 fail to convey accurate information regarding the impression, 

 simply because the new nervous routes have not been ex- 

 ercised to the same extent as the interrupted lines of 

 discharge. 



It also appears that among the jelly-fishes themselves 

 there are many and varying degrees of perfection in the 

 definiteness of their sensations, and in their aptitude to 

 respond to impressions made upon them. In a common 

 genus (Aurdia, see Fig. 49) of jelly-fishes, the irritability is 

 not nearly so distinctly localised nor so definitely transmitted 

 as in the last-mentioned case of Tiaropsis. In the latter 

 instance, the object of the polypite being able to move so 

 as accurately to indicate the irritated point is that of stinging 

 its prey, by means of an offensive apparatus placed at the 

 extremity of the mouth. So that the definite acts of the 

 animal have arisen in clear connection with a purposive 

 end, that of killing and seizing prey. But in other species 

 (e.g. Aurclia) the impulses travel in less definite fashion, 

 if we may judge from the results which follow stimulation. 

 A portion of the body of Aurclia, a very common species 

 of jelly-fish, when cut, as in one of Mr. Romanes' experi- 



