372 CHAS. W. HARGITT. 



the several modes of isolating the tissue cells the following were 

 employed: With hydroids the coenosarc may be forced out of 

 the perisarc by clipping off the hydranths and then stripping 

 the stems through clean fingers, or the ends of smooth forceps, 

 or similar device. Again, one may finely clip up the stems with 

 scissors and then still further reduce the cells by continuing the 

 operation in deep watch glasses or small beakers. A still further 

 mode was used, that of clipping up the stems with scissors and 

 later grinding the tissues under a smooth glass rod whose end 

 had been rounded in the flame, employing it as a pestle and a 

 watch glass as a mortar. One objection to this was the crushing 

 of the individual cells in many instances, and otherwise injuring 

 them. On the other hand there may be reason to believe that 

 such treatment is not really so serious an injury as might at 

 first sight appear, for as will be seen in some later discussion, the 

 shock may actually serve as a stimulus to hasten cellular de- 

 specialization and hence initiate regenerative processes. 



Cell dissociation having been effected the next method is to 

 arrange them in dishes where aggregation may take place. First 

 in this operation is the straining or filtering out of debris and such 

 fragments as are undesirable. This was done chiefly by pressing 

 the cells through bolting cloth. In my experiments it was found 

 that a better medium than silk bolting cloth was a fine meshed 

 cheese cloth, or a coarse meshed linen or cotton fabric, which was 

 softer and apparently more efficient. In a few cases in the earlier 

 experiments I merely placed the entire mass in watch glasses 

 and with a pipette carefully drew off most of the coarser stuff 

 and left the cells as free as such a process might leave them. On 

 the whole, the pressing process worked better and was more 

 expeditious. Following this operation the cells were left for a 

 time to settle and then the milky sediment was carefully drawn 

 off, when fresh water was added and the dishes set aside in 

 bowls surrounded by running water to ensure as constant a 

 temperature as could be had. 



The Experiments. 

 Podocoryne carnea. — This was the first species which came to 

 hand and proved one of the most responsive and convincing 



