250 



Royal Society . 



case of a specimen which \\ as 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 per- 

 formed ; and even in the genus Sarsia its occurrence is compara- 

 tively rare. It never begins spontaneously, 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 ex- 

 haustion. 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 excita- 

 ble tissues of all the Medusre 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. Presh water is quickly fatal to 

 Medusie. 



§ 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 destruction of 

 their physiological continu- 

 ity is in the highest degree 

 astonishing. 



(rt) Suppose the annexed 

 diagram to represent Sar- 

 sia in projection, the lines 

 being cuts. It is evident 

 that a stimulus originating 

 at any point a in the mar- 

 gin cannot radiate its in- 

 fluence throughout the nec- 

 tocalyx, except by traversing 

 the course of the dotted 

 line ; yet in a specimen so 



cut tlie spontaneous contractions are as synchronous over the 

 entire nectocalyx as they are in unmutilated specimens. Further, 



