GERM CELLS OF COELENTERATES 3 



this as the germinal zone, chiefly on account of the abundant 

 food supply in a region so close to the polyps, thus calling atten- 

 tion to the essential relation between germ-cell formation and 

 abundant nourishment. This region is also near the growing 

 zone and the germ cells were believed to arise only from young 

 cells. However, these young cells were regular ectoderm cells 

 and not a special kind of cell, for he says: 



One can say positively, that the same small egg cells] are visibly 

 distinguishable in no way from other yomig ectoderm cells, for one 

 can always recognize the place at which later a germ zone will form 

 and can demonstrate that in that place are no cells which could be so 

 designated [as germ cells]. The germ cells are therefore not in this 

 case definitely contained in the colony from the beginning and dif- 

 ferentiated only at the time of sexual maturity, but they ai'ise only at 

 this time out of a growing mass of young cells. 



This essential relation between the origin of germ cells and an 

 abundant food supply so positively stated by Weismann and 

 since then abundantly confirmed by other authors, he did not 

 maintain in later publications. In like manner, his own obser- 

 vations and demonstrations upon the origin of the germ cells 

 from the ordinary cells of the hydroid body, both of ectoderm and 

 of entoderm, he later discarded in favor of a theoretical view 

 that they came from a peculiar and self-perpetuating tissue or 

 substance, the germ substance. Weismann studied other species 

 of Eudendrium, notably E. capillare, in which he found egg cells 

 only in the entoderm. Their origin and growth, he says, must 

 therefore be from and in the entoderm alone, ''since it is incon- 

 ceivable, that otherwise one should never find egg cells in the 

 ectoderm." 



C. W. Hargitt ('04) studied several species of Eudendrium. 

 He found the egg cells of E. racemosum both in ectoderm and 

 entoderm, but believed the entoderm to be the place of origin, 

 since it contained the smaller cells. The same was true for E. 

 dispar and E. ramosum. Weismann's account for E. capillare 

 was entirely confirmed, viz., that egg cells were found always 

 and only in the entoderm, and a similar condition existed in E. 

 tenue. This author finds that ''the ova arise in hydroids by 



