366 0. C. Glaser and C. M. iSparrozu 



or the nematocysts, results in the abstraction of water, and that 

 for this reason, the former shrivel and the latter remain intact. 

 Why some of the nematocysts fail to discharge when the majority 

 explode, will be discussed in connection with later experiments. 



EXPERIMENTS WITH THE TENTACLES AND ACONTIA OF METRIDIUM 



The results of Grosvenor, and those just described, lend strong 

 support to the idea that the discharge of nematocysts is due to 

 osmosis, and while none of our experiments seem to indicate that 

 this idea is erroneous, the study of the living tentacles and acontia 

 of Metridium, shows that the matter is not quite as simple as 

 might be supposed. In nematocyst-bearing tissues, another fac- 

 tor must be reckoned with, the living nematocyte, the cell which 

 makes the nematocyst and encloses it. 



The living tentacles, as well as the acontia of Metridium may 

 be removed without discharging the nematocysts; this can be done 

 very easily in the case of the tentacles, not quite so easily with the 

 acontia, but even in this instance, an abundance of intact threads 

 or pieces of threads, is readily obtained. These can then be 

 treated in various ways, and the behavior of the nematocysts 

 studied. 



In certain media, many of the nematocysts leave their natural 

 positions in the mother tissue, but do not discharge; media of 

 much higher osmotic pressure than sea water, may bring about 

 discharge, and heat, electricity and mechanical pressure are effec- 

 tive. At first sight these results seem to be strongly antagonistic 

 to the osmotic theory, but careful analysis of them, either changes 

 all of these data into positive supports or at least disarms them. 



In the following table is given a resume of the details of the ex- 

 periments on the effects of various media and stimuli on living 

 nematocyst-bearing tissues. The material used is mentioned in 

 the first column; the treatment given it, in the second; whereas the 

 effects on the nematocysts are recorded in the third and fourth 

 columns. The word extrusions is used to designate those in- 

 stances in which nematocysts, without exploding, left their normal 

 positions in the mother tissue. Such extrusions are due either to 



