The Physiology of Nematocysts 375 



diluted still further. It follows from this that the pressure neces- 

 sary to explode nematocysts instantaneously varies with the indi- 

 vidual capsule, and as these differences occur in nematocysts pre- 

 pared by the digestion as well as the maceration methods, it is 

 safe to conclude that the observed facts are normal. 



It is conceivable that the porosity of the capsular wall may 

 vary with its age, or may vary independently of this, and the same 

 thing is true of the intracapsular contents. Either of these pos- 

 sibilities would account for the facts. It is also true that other 

 slight differences in the construction of the capsules might affect 

 the pressure needed to explode them, and possibly also, not all 

 of them are in equally good working order. In the eversion of a 

 barbed thread, like that characteristic of the nematocysts of Me- 

 tridium, it would seem that there is ample opportunity for en- 

 tanglements, capable of being loosened or broken only by in- 

 creased pressure from within. 



APPLICATIONS OF THE OSMOTIC THEORY TO .SOLIDS AND 

 CCELENTERATES 



Molids 



The experiments described can leave no doubt that osmotic 

 pressure can account for all of the observed facts. The question 

 now arises, why do the nematocysts of nudibranchs discharge on 

 coming into contact with sea-water, whereas those of coelenter- 

 ates remain intact .^ 



While enclosed within their mother cells in the coelenterate, the 

 nematocysts must be osmotically neutral toward their cellular 

 environment and since they themselves are neutral toward sea- 

 water, it follows that we must consider the nematocyte also osmot- 

 ically neutral toward its external environment. This neutrality 

 must be disturbed by the sojourn of the nematocysts within the 

 bodies of the nudibranchs, or some other factor must enter to 

 counteract it. After careful consideration of the possibilities that 

 suggest themselves, we have discarded all but one: by slow trans- 

 fusion, the contents of a nematocyst osmotically neutral toward 



