486 
SEITARO CxOTO 
are truly ectodermal in nature. The germ cells are very numer- 
ous in the endoderm, although it is hard at this stage to distin- 
guish them individually from cells that remain definitively endo- 
dermal. They are however characterized by large vesicular nuclei. 
The gonophore grows larger, the inner ectoderm spreads out more 
and more, the germ cells passing through the supporting lamella 
come to lie in the inner ectoderm, and the endoderm rises up in the 
center of the bud to form the spadix, until the stage represented 
in fig. 17 is reached. A very conspicuous feature of this stage is 
the inner ectoderm. This forms a conspicuous deeply staining 
mass in and around the original opening by which it communi- 
cated with the outer ectoderm. In the section here reproduced 
the opening has been largely filled by a membranous septum of 
supporting lamella. Numerous small nuclei are scattered between 
the germ cells, staining more deeply and diffusely than the latter, 
and doubtless belong to the cells of the inner ectoderm. A similar 
layer of the inner ectoderm capping the top of the germ cells is de- 
scribed and figured by Goette in Hydractinia echinata^^ The en- 
dodermal lamella has become much compressed and dense, but the 
nuclei can still be distinctly seen . In this as in the previously figured 
stage the outer ectoderm is greatly thickened at the top of the 
gonophore; this becomes less conspicuous in later stages and may 
entirely disappear at last. In fig. 18 is reproduced a male gono- 
phore which is nearly ripe, and there is no difficulty in connecting 
it with the previously described stage; for the same parts are 
present in both, though much altered. The spadix has become 
greatly elongated and irregularly club-shaped, the tall endoder- 
mal cells presenting a typical epithelial arrangement, and enclos- 
ing a central cavity directl}^ continuous with that of the blastostyle. 
The endodermal lamella is exceedingly thin, but can be clearly 
distinguished as a distinct layer separating the two supporting 
lamellae enclosing it and directly continuous with the endoderm 
of the spadix at the base of the gonophore; the nuclei can be ob- 
served with extreme difficulty if they are present at all. The open- 
ing between the inner and the outer ectoderm was present in a 
" Goette: '07, p. 73, pi. 6, fig. 132. 
