380 O. C. Glaser and C. M. Sparrow 



nematocysts were then discharged by fixing the preparation in 

 sublimate acetic. The tissues which had been "shot" in this 

 way were then sectioned, and in several regions it was possible 

 to trace the filaments of the nematocysts through the epidermis 

 into the muscle and connective tissues below. Most of the threads 

 however, did not enter the tissues, but seemed to have been warded 

 off, and in the sections lie tangential to the epidermis. This is 

 what might be expected, for unless a filament penetrates while 

 it is at the height of its speed, it fails to make a puncture at all, 

 for the extreme end is everted too feebly, just as Mobius says. 



Direct observations on the behavoir of the nematocysts of Mon- 

 tagua, while still enclosed within the cnidocysts, are much more 

 favorable for the elucidation of this question. We have reported 

 in an earlier section that the nematocysts may explode before the 

 cnidocyst bursts, and that the discharged filaments are capable 

 of penetrating through their enclosing membrane.^ The length 

 of the discharged filament; the position of the nematocysts inside 

 the cnidocyst, and the diameter of the cnidocyst, make it abso- 

 lutely impossible for the filaments to penetrate the membrane at 

 any other than the early stages of eversion. The cnidocysts are 

 not large enough to allow anything else; nevertheless the filaments 

 penetrate them, which is exactly what they should do if the osmotic 

 theory of discharge, and the considerations brought forward in 

 the preceding paragraphs, are correct. 



SUMMARY 



1 The material used consisted chiefly of the living tentacles 

 and acontia of Metridium, and nematocysts, isolated, by diges- 

 tive and other methods, from Metridium and Physalia. 



2 The discharge of nematocysts is due to internal pressure. 

 This pressure may be raised to the exploding point by osmosis and 

 by distortion. 



- Two months after this paper was written Toppe (Zoologischer Anzeiger Bd. xxxiii, Nos. 24/25) 

 published an account of his very careful observations on the manner in which nematocysts dis- 

 charge, and showed conclusively that the nettling threads are able to puncture the chitinous 

 covering of a Corethra larva. 



