PORIFERA, CCELENTERATA, VERTEBRATA 87 



stimulus from which results the formation of the 

 gonophore" (Hargitt, 1904 a, pp. 261-262). 



Hydractinia has been investigated by van 

 Beneden (1874), Weismann (1883), Bunting (1894), 

 and Small wood (1909). Weismann considered the 

 ectoderm of the blastostyle to be the probable place 

 of origin of the germ cells in this genus. Bunting 

 (1894) was unable to trace the ova to this layer, 

 although she found them to be quite abundant in 

 the entoderm of the blastostyle, even before the gono- 

 phore appeared. According to this author the ova 

 apparently arise in the entoderm of the blasto- 

 style, and "reach maturity on the outside wall of 

 the spadix, lying between the endoderm and the 

 inner layer of the bell nucleus. The spermatozoa 

 arise from the inner layer of the bell nucleus ; we 

 see that they are, therefore, ectodermal in origin " 

 (p. 228). 



These results are not confirmed by the researches 

 of Small wood (1909), who finds that the eggs arise 

 in the entoderm in any region of the polyp, at the 

 base, the side of the polyp, or in the gonophore. 

 They may be distinguished from other entoderm 

 cells by the larger size of the nucleus. 



In Pennaria cavolini the germ cells arise in the 

 ectoderm, according to Weismann (1883), and this 

 conclusion is confirmed for the ova by Hargitt 

 (19046). In P. tiarella the germ cells are likewise of 

 ectodermal origin (Smallwood, 1899, Hargitt, for 

 the ova, 19046). The eggs of this species arise 

 in the ectoderm of the manubrium and grow by 



