GERM CELLS OF COELENTERATES 11 



In addition to the line of evidence just presented, we have 

 direct observations upon the entire germ-cell cycle of some 

 hydroids from their earUest differentiation. Some of the thirty 

 or more species studied by Goette ('07) give very clear evidence 

 of the method of origin of germ cells. In Podocorjme germ cells 

 arise from both ectoderm and entoderm; in Corydendrium para- 

 siticum the egg cells are formed from ordinary entoderm cells by 

 division, a basal egg cell and a distal epithelial cell resulting, and 

 only this method of formation is applicable in this species. A 

 similar division takes place in Clava, and Goette says, "no doubt 

 exists, that the egg cells of Clava multicornis proceed only from 

 transformed half entoderm cells." He observed epithelial cells 

 dividing, one half forming the egg cells of Sertularia argentea, 

 Gonothyraea loveni, Obelia longissima, and the sperm cells of 

 Eudendrium. In Obelia geniculata the eggs develop only in the 

 medusae by the transformation of entire entoderm cells. Small- 

 wood ('09) traced the egg cells of Hydractinia echinata back to 

 single entoderm cells which underwent no division, but trans- 

 formed directly into oocytes. Campanularia fiexuosa produces 

 its eggs by a similar transformation of entire entodermal epi- 

 thelial cells or from the basal half of a divided entoderm cell, the 

 distal end of which persists as an epithelial cell (G. T. Hargitt, 

 '13). The author ('16) also observed egg cells typically arising 

 from half entoderm cells in Clava leptostyla, though occasionally 

 from ectodermal interstitial cells. 



Such observations upon a number of species by different 

 investigators leave no' doubt of the entire normality of the 

 described transformation of tissue cells into germ cells. In such 

 cases there can have been no differentiation and segregation of 

 germ cells in the early ontogeny, for they came from functional 

 tissue cells, a portion of which continued as a tissue cell. Such 

 a cell is a specialized cell and not a latent germ cell. In certain 

 Hydrozoa, therefore, the origin of germ cells has been precisely 

 determined and an early differentiation shown to be impossible; 

 in the absence of positive evidence to the contrary, it would 

 probably be fair to believe that none of the Hydrozoa show a 

 differentiation of germ cells till sexual maturity approaches. 



