228 BUNTING. [Vor. IX. 
CONCLUSIONS. 
The gonophore of Hydractinia arises through the protrusion 
of the ectoderm and endoderm caused by a multiplication of 
cells in both layers. The bell nucleus does not originate by 
invagination, but from a few ectodermal cells, that take up a 
position between the ectoderm and endoderm, and increase, 
forming subsequently two layers of cells. 
The ova are first observed in the endoderm of the blasto- 
style, thus, apparently endodermal in origin ; 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. 
The medusa-bud of Podocoryne arises as a protrusion of the 
ectoderm and endoderm, caused by an increase in the cells of 
both layers. The bell nucleus is formed from ectoderm, not 
by invagination, but consists at first of a solid plug of cells; 
later, by separation of these cells there is formed two layers 
with an intervening space. 
The ova are first seen in the endoderm of the manubrium, 
and they reach maturity in the ectoderm of the manubrium. 
The spermatozoa arise in the ectoderm of the manubrium, 
and reach maturity in the same position, thus, they are 
ectodermal in origin. 
The ovum of Hydractinia is laid at a definite period of the 
day ; two polar globules are formed; both leave the surface of 
the egg at the beginning of segmentation. Segmentation is 
total and equal. The endoderm originates through multipolar 
delamination, beginning at about the sixteen-celled stage, and 
cells continue to delaminate for some time. By breaking down 
of endoderm cells, the coelenteric cavity arises, at the same 
time the two layers are sharply differentiated and the support- 
ing lamella appears. The embryo becomes elongated and 
ciliated ; attached to a substratum by its blunt anterior end. 
The tentacles appear as solid endodermic outgrowths  sur- 
rounded by ectoderm. ‘The mouth is formed by the coelen- 
