The Physiology of Nematocysts 379 



nettles are due to the numerous poisoned threads which surround 

 and penetrate the victim. Mobius distinctly opposes this view 

 as well as others which are current. For instance he considered 

 the idea that the hairs on the filaments are "back hooks," a mis- 

 taken one, not only because in the ripe thread they stand out at 

 right angles, but also because they are too delicate to serve the 

 function attributed to them. Mobius might have added that many 

 types of functional nematocysts are devoid of these barbules. 



As for the ability of the thread to penetrate into the tissues of 

 the victim, Mobius considered this impossible, in the first place 

 because the thread "unrolled" too slowly, and in the second place, 

 because its point does not strike the victim. In fact, the point is 

 the last portion of the thread to be everted, and it is, of course, cast 

 out with less force than any other part. The great delicacy of 

 the point was also offered as evidence against the validity of the 

 current belief. 



The nettling sensations produced by nematocysts, Mobius did 

 not attribute to the minute punctures made by the filaments, 

 but to the fact that these are saturated with some chemical, which 

 on coming into contact with the skin, produces irritation. This 

 chemical remained undetermined, but relying entirely on micro- 

 chemical tests, Mobius concluded that it is neither formic acid, 

 nor any other acid. 



The existence of hypnotoxin seems to be fairly well established, 

 whereas there is considerable doubt about the inferred "Reiz- 

 gift." All the phenomena which the "Reizgift" could explain, 

 seem to me to be explicable on the assumption that the filaments, 

 contrary to Mobius' conception of their powers, do actually pene- 

 trate the tissues. The idea does not seem to have occurred to him 

 that a thread might penetrate a tissue before being completely 

 everted; he does not seem to have realized at what immense pres- 

 sures the discharges occur; nor, if he knew of such instances, did 

 he recall that, given sufficient velocity, a stem of hay will shoot 

 through a pane of glass. 



Observations, as well as experiments, bearing on the penetrat- 

 ing power of the filaments were made. Thus the acontia of 

 Metridium were placed on fresh tissue taken from a clam, and the 



