GERM CELLS OF COELENTERATES 25 



the presence of germ cells. The later work on dissociated cells 

 gives clear evidence on this point. DeMorgan and Drew can 

 recognize and follow the isolated ectoderm and entoderm cells 

 and ". . . . in addition such structures as nematocysts, 

 ova and broken down cells, all of which are subsequently ab- 

 sorbed and played no part in the future development." C. W. 

 Hargitt also finds that the presence of germ cells in regenerating 

 masses does not influence the behavior: '' Indeed, in those cases 

 in which egg cells were present they took no part whatever in 

 later regenerative activity, either degenerating or being absorbed 

 as yolk material." So far from the regeneration being con- 

 ditioned upon the presence of germ cells, the latter serve no 

 purpose but to act as food; growth and differentiation are the 

 result of the activity of the tissue cells alone. Since these 

 observations have been confirmed by a number of workers, it is 

 manifestly false to consider regeneration to depend upon germ 

 cells in these plasmodia. There would appear, likewise, to be 

 no ground for assuming any regeneration to be dependent upon 

 germ cells. 



The claim of DeMorgan and Drew, of the retention of their 

 distinct structure by the isolated cells, and a later rearrange- 

 ment to produce the regenerated structures, is not confirmed 

 by any of the other workers. The latter agree in being able to 

 follow the isolated cells through a gradually decreasing sharpness 

 and a final coalescence into a common mass. No doubt occa- 

 sional cells persist, but the observations clearly show the fusion 

 of the cells into a multinucleate mass. From such a mass a 

 development occurs which parallels the normal development from 

 the egg. 



These experiments give such striking and clear-cut results that 

 one is enabled to draw very definite conclusions. Tissue cells 

 have actually been followed through the process of despeciali- 

 zation to an embryonic condition; such embryonic cells behave 

 as any other group of similar cells, and develop a variety of 

 structures which become differentiated and specialized in such a 

 way as to produce a complex, normally organized, and functional 

 individual. The totipotency of the tissue cells of the hydroid is 



