24 GEORGE T. HARGITT 



normal, with tentacles, mouth, hypostome, and other structures. 

 In these changes ''we apparently have .... a plain case 

 of despecialization of tissue elements and their union to form 

 masses of totipotent regenerative tissue." Wilson discusses the 

 question as to whether the tissue cells may not merely retain 

 their specificity and later produce only cells of the same sort. 

 By following the isolated cells with the microsdope it was possible 

 to observe the change of the tissue cells from their typical 

 appearance to that of embryonic cells, and their fusion into a 

 mass. The retention of their original specificity seems highly 

 improbable. A histological study of sections of the coalesced 

 cells showed the cells, first, as embryonic in appearance, and, as 

 regeneration proceeds, they undergo changes similar to those 

 seen in normal development and specialization. DeMorgan 

 and Drew ('14), in similar experiments, for the most part con- 

 firmed Wilson, but did not obtain hydranths from the regenerating 

 masses. They differ from Wilson in thinking the cells are segre- 

 gated and rearranged and do not form syncytia by despeciali- 

 zation. They also state their behef that their cell masses are 

 abnormal and pathological, but this does not appear to be the 

 case, as C. W. Hargitt ('15) has pointed out in some detail. 

 This latter author confirmed Wilson's observations in practically 

 every respect, and also noted in detail the behavior of cells 

 immediately after their isolation. The identification of the 

 different cells was easily made, but the characteristic features 

 gradually became less marked and finally disappeared as the 

 cells merged into a common mass. ''They have become de- 

 specialized into potentially embryonic cells, and probably from 

 this change have acquired their regenerative capacities." 



In discussing these experiments, Hegner ('14) claims there are 

 always germ cells present, which would exlain the regeneration 

 from the masses of cells, and therefore a continuity of germ 

 plasm exists in these phyla. He does not attempt to explain 

 the de-differentiation actually observed to occur, though this is 

 a very significant fact and one that cannot be ignored. For, if 

 tissue cells may become embryonic and form other cells and 

 tissues by later differentiation, there is no reason for assuming 



