GERM CELLS OF COELENTERATES ' 7 



planula develops, these interstitial cells divide to produce such 

 groups as the one shown in figure 3; at the same time the entoderm 

 cells assume a definite epithelial form. During the progress of 

 the development of the planula the entodermal interstitial cells 

 decrease in number, nematocysts are formed from some of them, 

 and others become elongated, as shown in figure 4. Some of these 

 spindle-shaped cells extend, or move, toward the free surface of 

 the entoderm and have the form and appearance of gland cells. 

 None of the entodermal interstitial cells remain in the form shown 

 in figure 2, and none of them, in the older planulae, displaj^ the 

 characteristics of germ cells. During these changes in the 

 entoderm there are very few ectodermal interstitial cells produced 

 (none were present in the region of the planula from which the 

 figure was made), and through the entire history of the planula 

 there are no germ cells in the ectoderm. 



Thus, by the time the planula has been perfected, there are no 

 cells in the ectoderm or entoderm which have even the remotest 

 resemblance to germ cells. The almost complete absence of inter- 

 stitial cells from both germ layers of the completed planulae, 

 and the formation of nematocysts from most of these, renders it 

 certain that prunordial germ cells are not present at this stage. 

 Consequently, the cells which resemble those interpreted as germ 

 cells by Wulfert and Harm are not such, but differentiate into 

 specialized cells of the body. 



There are some differences in the formation of the morula in 

 Gonothyraea loveni, but once the solid mass of cells is produced 

 the development is so similar to that of Campanularia it has not 

 been thought necessary to describe and figure this form. But it 

 may be said that at no stage could I find even a single cell in Gono- 

 thyraea which showed the characteristics of a germ cell. I am 

 forced to beheve, therefore, that Wulfert described as germ cells 

 merely interstitial cells which were undergoing differentiation into 

 ganglion cells, gland cells, or some other specialized cell element. 

 Certainly, if primordial germ cells were characteristically present, 

 one should be able to find them, but this study of similar stages 

 of the same species on which Wulfert worked gave no evidence 

 of their presence. 



