486 



On the Locomotor System of Medusce. 



[Jan. 11, 



nervous sliock (such as that caused by a sudden jar on an anvil or 

 violent shaking in a bottle of sea-water) often has the effect of destroy- 

 ing coordination for some time after spontaneity returns. 



yi. Poisoi^s. 



As this abstract is already too long, I will here only enumerate the 

 poisons I have tried, without entering into the details of their action. I 

 may say, however, in general terms, that in almost every minute parti- 

 cular the effects of the various poisons I have hitherto tried are precisely 

 identical in the case of the Medusae and in that of the higher animals. 

 In my paper the effects of each of the following poisons are treated 

 at length, viz. — chloroform, nitrite of amyl, caffein, strychnia, veratrium, 

 digitalin, atropia, nicotin, alcohol, and cyanide of potassium. The details 

 of this part of the inquiry are rendered particularly valuable from the 

 fact that, in the case of Sarsia, we have the means of testing the com- 

 parative influence of any poison on the central, peripheral^ and muscular 

 systems respectively ; but it is needless on the present occasion to occupy 

 space with a description of the methods — it being enough to say that the 

 effects of the various poisons on these respective systems are uniformly 

 such as occur in the case of the higher animals. In one important par- 

 ticular, however, the actions of nearly all the above poisons on the Medusae 

 differ from their actions on the higher animals ; for there is no poison in 

 the above list which has the property, when applied to the Medusae, of 

 destroying life till long after it has destroyed all the signs of irritability. 

 I think this anomaly is to be explained by two considerations. First, 

 the Medusae present to the action of the central nerve-poisons no nerve- 

 centres which are of vital importance to the organism ; and, consequently, 

 such poisons are here at liberty, so to speak, to exert their full influence 

 on all the excitable tissues, without having the course of their action 

 interrupted by premature death of the organism. Second, the method 

 of administering the above-mentioned poisons to the Medusae was very 

 different from that which we employ when administering them to other 

 animals ; for, in the case of the Medusae, the neuro-muscular tissue is 

 spread out in the form of an exceedingly tenuous sheet, so that when 

 the animal is soaking in the poisoned water, every portion of the excitable 

 tissue is equally exposed to its influence. And that the action of a 

 poison is greatly modified by such a difference in the mode of its ad- 

 ministration, has recently been proved by Professor Gamgee, who found 

 that when a frog's muscle was allowed to soak in a solution of vanadium 

 &c. it lost its irritability, while this was not the case when the poison 

 was administered by means of the circulation. 



Eresh water acts as a deadly poison to the Medusae. The naked- 

 eyed species usually cease their movements the instant tliey touch the 

 fresh water, and are killed by it, not, indeed, instantaneously as Agassiz 

 supposed, but in the course of a few minutes. The covered-eyed species 



