376 O. C. Glaser and C. M. Sparrow 



sea-water, may be changed, so that it becomes capable of absorb- 

 ing water, and consequently of raising its internal pressure to 

 the exploding point. To test this idea, isolated nematocysts 

 of Metridium were treated with a saturated salt solution for four 

 days. After this time sea-water, which is osmotically neutral to- 

 ward freshly isolated nematocysts, was as effective in bringing 

 about discharge as distilled water is when applied to unmodi- 

 fied capsules. 



Coelenterates 



A comparison of the results obtained from isolated nematocysts, 

 and from those imbedded in their living mother tissues, suggests 

 that the explanations which hold good for the former class hold 

 equally good for the latter; that in the one case we are dealing 

 with an osmotic interchange directly between the capsule and its 

 surrounding medium; in the other case between the nematocyte 

 and the medium, and that the permeability of the cell to the various 

 reagents used, is such that for practical purposes the nematocyte 

 is non-existent. It must be apparent that in most cases it is im- 

 possible to show that this, as a generalization, is incorrect, never- 

 theless, we believe that it is incorrect, and that the nematocyte, 

 the mother cell of the nematocyst, has something to do with its 

 discharge, possibly not under all circumstances (see Tables I 2nd 

 II) but certainly under some, and perhaps always when the 

 nematocyst is discharged in response to stimuli normal in the 

 lives of ccelenterates. 



The efficacy of the nematocyte as a factor in the normal dis- 

 charge of a nematocyst can be shown in at least three ways. A 

 saturated solution of sodium chlorid is incapable of bringing about 

 the explosion of isolated nematocysts. This, however, is not true 

 when the same solution is applied to the living tentacles and acon- 

 tia of Metridium. (Table I.) Under this treatment a complete 

 discharge of all the nematocysts occurs. The alternating current, 

 when applied to isolated nematocysts, is ineffective, but when ap- 

 plied to fresh tentacles and acontia, it brings about the discharge 

 of all the nematocysts present. 



These two experiments suggest that the cell is effective, and that 



