Dr. A. Waller on the means by which the Actinirc kill their Prey. 227 



Besides these principal and more general characters, those also which 

 distinguish the vertebrae of the several regions of the spine, together 

 with the specialities of the atlas and axis, and of other individual 

 vertebrae, are pointed out and described. 



April 14, 1859. — Sir Benjamin C. Brodie, Bart, President, in the 



Chair. 



"On the means by which the Actinice kill their Prey." By Au- 

 gustus Waller, M.D., F.R.S. In a Letter to Dr. Sharpey, Sec. R. S. 



In the ' Proceedings of the Royal Society' for the 18th November, 

 p. 478*, I perceive that Dr. McDonnell's fresh observations on the 

 Actiniae have led him to abaudon the opinion which he had been 

 disposed to entertain as to their possessing electrical powers similar 

 to those of the torpedo. During a stay at the sea-side in the winter 

 of 185/-58, I put in hand some experiments for the purpose of 

 testing the supposed electrical powers of these animals, which, as 

 I some months since mentioned to you, led me to negative con- 

 clusions relative to their siderant power. Dr. M'Donnell's recent 

 observations having removed any occasion of controversy, I will 

 briefly mention the results that I obtained. 



The most interesting fact observed by Dr. M'Donnell is the 

 contraction of the galvanoscopic frog when the Actinia seized upon 

 the sciatic nerve. On repeating this experiment, I was particularly 

 struck by the uncertainty and irregularity with which these con- 

 tractions were obtained, being sometimes very strong, while at others 

 they were imperceptible notwithstanding all the precautions that I 

 could take as to the frogs being fresh caught and irritable, besides 

 attending to the rules laid down by Matteucci. 



On the other hand, when, in lieu of a galvanoscopic frog, I pre- 

 sented a Nereis to the Actinia, the result was invariably the death of 

 the animal. The effect of the Actinia's grasp upon the Annulata is 

 mortal, although the retention may not have been allowed to exceed 

 a few moments. The first symptom which I observed was that of 

 writhing, as if the creature were in great pain, and which in the 

 most marked cases was succeeded by paralysis with flaccidity of the 

 muscles, like a frog acted upon by woorara. The action of the 

 dorsal vessel, which still persisted long after the loss of voluntary 

 power, was very irregular and segmental, the vessel being bloodless 

 and inert at intervals. 



It appeared indifferent whether the cephalic or the caudal ex- 

 tremity of the Nereis was attacked by the Actinia, similar symptoms 

 being produced in both cases. 



In order to ascertain how far these symptoms were produced by 

 electricity, I subjected the Nereis enclosed in a glass tube to some 

 violent shocks by means of an electro-magnetic machine, which were 

 merely productive of a slight temporary inconvenience to the animal, 

 unattended by any after evil effects. It is most remarkable what 

 powerful electric action these creatures are susceptible of enduring 

 * Ann. Nat. Hist. ser. 3. vol. iii. p. 304. 



15* 



