GERM CELLS OF COELENTERATES 5 



Harm does not describe the formation of ganglion or nettling 

 cells in Clava, but his germ cells follow the same course as the 

 ganglion cells of Wulfert in Gonothyraea, and Wulfert never refers 

 to the spindle-shaped cells as germ cells. It seems clear that 

 both these investigators are dealing with interstitial cells. Wul- 

 fert's results would suggest that what Harm called germ cells 

 were in reality differentiating ganglion cells. Wulfert states that 

 his primordial germ cells arise from interstitial cells, but the 

 evidence he presents in favor of considering these as germ cells 

 is not convincing. The determining characteristic, to him, is the 

 more deeply staining cytoplasm, and this, I believe, cannot be 

 considered a sufficient criterion, as I have pointed out in another 

 place (G. T. Hargitt, '16). 



Stschelkanowzew ('06) describes germ cells as present in late 

 cleavage stages of Cunina proboscidea. While the embryo is a 

 solid mass of cells and the ectoderm and entoderm are being sepa- 

 rated as layers of a single cell in thickness, he finds one or two 

 cells between the ectoderm and entoderm layers, but neither in 

 description nor in figures does he specify the characteristics of 

 these cells. Their size, form, color reaction, and the size of 

 nucleus seem to be the same for the ectoderm cells, the position 

 alone is different. In this instance, also, we have to do either 

 with the formation of interstitial cells or with the completion of 

 the formation of the cells of the central solid mass. Precisely 

 the same process will presently be described for the formation 

 of embryos of Tubularia. 



There is no question of the early formation of interstitial cells; 

 these have been found, described, and their differentiation followed 

 in Hydrozoa by various authors. For example, Schneider, ('90) 

 noted the characteristic and early appearance of interstitial cells 

 in Hydra, and their later transformation into ganglion cells, 

 nematocysts, and germ cells. Morganstern ('01) traced the 

 development of Cordylophora through the larval period, and 

 identified the ganglion and nettling cells produced from inter- 

 stitial cells, but did not find any evidence of germ cells in larvae 

 or young polj^DS. The germ cells arose from ectodermal inter- 

 stitial cells at the time of sexual maturity. Schneider and Mor- 



