The Physiology of Nematocysts 365 



until they have been almost completely extruded, when the nemat- 

 ocysts begin to shoot into the visible portion, either one by one, 

 or in groups. When this has happened, the cnidocysts leave their 

 positions at the mouth of the cnidopore, usually on account of the 

 movements of the animal or of its appendages, and may float freely 

 in the vv^ater nearby, or may remain adhering to other regions of 

 the ceras. 



The nematocysts so extruded, in many instances discharge in- 

 side of their enclosures and as their threads penetrate through the 

 wall of the cnidocyst, this may come to resemble a "sperm-bundle," 

 with filaments radiating in all directions. Ultimately the cysts 

 burst, and set free their discharged contents. This, however, is 

 not the usual history — ordinarily the bursting of the cnidocyst and 

 the explosion of its nematocysts take place at the same instant. 

 The questions therefore arise: Why do the cnidocysts burst, and 

 why do the nematocysts discharge ? There are involved no liv- 

 ing tissues which might be responsible; the nernatocysts are not 

 living things, and their enclosing cnidocysts are also dead. 



A simple experiment gives the answers. If Montagua is stim- 

 ulated thermally in a concentrated sugar solution, the elimination 

 of cnidocysts takes place as described, only as soon as they come 

 into contact with the surrounding medium they shrivel. None of 

 the cysts burst, and none of the nematocysts discharge. If now 

 the sugar solution is replaced by distilled water, the cnidocysts 

 swell and burst, and the nematocysts discharge. Discharge, how- 

 ever, is rarely complete; a few nematocysts in every collection of 

 them fail to discharge under circumstances under which the major- 

 ity explode. 



If this experiment is modified, and the elimination is forced to 

 occur in distilled water, the bursting of the cnidocysts^and the 

 discharge of the nematocysts take place so quickly, that it is im- 

 possible to be more than aware of the processes. Even under these 

 conditions some nematocysts may remain undischarged. 



The most plausible explanation of these results is that the burst- 

 ing of the cnidocysts, and the discharge of the nematocysts are 

 due to absorption of water; that introduction into a medium of 

 higher osmotic pressure than the contents of either the cnidocyst. 



