1875.] 



Locomotor System of Medusce. 



147 



hour. I never but once saw a similar motion in a perfect animal, and 

 this was in the case of a specimen which was being poisoned with iron- 

 rust. The motion may, I think, be explained by supposing that the 

 various systems of muscles are contracting without coordination ; but why 

 they should sometimes do this in response to electrical stimulation, and 

 why, when they do this, they should continue the action so long, these 

 questions I cannot answer. In no other genus of the Medusae have I 

 ever seen a similar or corresponding action performed ; and even in the 

 genus Sarsia its occurrence is comparatively rare. It never begins spon- 

 taneously, and it appears to be most readily evoked by submitting the 

 paralyzed nectocalyx to a number of shocks, either from the direct or 

 the induced current, in somewhat rapid succession. When it does occur 

 it is always continuous, i. e. it never spontaneously recommences after 

 having once ceased. When its period of duration is prolonged, the 

 shivering motions become feebler and feebler, until they eventually fade 

 away into quiescence. The animal is then quite insensible to all further 

 stimulation: the tissues appear to have died from exhaustion. These 

 shivering motions may also be caused in Sarsia by slightly acidulating the 

 water in which the mutilated nectocalyx is suspended. 



§ 3. In their behaviour towards chemical stimuli, the excitable tis- 

 sues of all the Medusae conform in every respect to the rules which are 

 followed by the nervo-muscular tissues of higher animals. Both the severed 

 margins and the mutilated swimming-organs, as well, I may add, as 

 severed polypites and tentacles, respond to applications of various acids, 

 solutions of various metallic salts, alcohol, ether, glycerine, &c. Fresh 

 water is quickly fatal to Medusae. 



§ 4. My observations upon thermal stimulation are, for the present, 

 reserved. 



IV. Section. 



§ 1. The extent to which the swimming- organs of Medusae may be 

 mutilated without suffering de- 

 struction of their physiological 

 continuity is in the highest degree 

 astonishing. 



(a) Suppose the annexed dia- 

 gram to represent Sarsia in pro- 

 jection, the lines being cuts. It is 

 evident that a stimulus origina- 

 ting at any point a in the mar- 

 gin cannot radiate its influence 

 throughout the nectocalyx, except 

 by traversing the course of the 

 dotted line ; yet in a specimen so 

 cut the spontaneous contractions 

 are as synchronous over the entire nectocalyx as they are in unmutilated 



