53 
the polypes at a short distance behind the distal extremity. They 
may he seen to consist externally of an investing sac (ectotheque), 
which is a simple extension of the ectoderm of the polype, like it 
containing thread-cells, and totally destitute of polypary. 
Immediately within this is another sac (sporosac), in which the 
indications of decided structure are very obscure. The second sac 
immediately invests the mass of ova or spermatozoa which occupy 
the space between its wall and a well-developed manubrium, which 
lies in the axis of the sac. The manubrium is a simple diverticulum 
of the endoderm of the polype, its cavity freely communicating with 
that of the latter. I could find no evidence of an ectodermal layer 
upon it. There are no gastrovascular canals. 
I have not succeeded in making out any further structure in the 
gonophore of Hydractinia, which may be assumed as a type of the 
simple gonophore. 
Hydractinia echinata is strictly dioecious, the male and female 
gonophores being always separated, so as to occupy distinct colonies. 
Coryne ramosa. 
-The gonophores here belong to the simple type. They are borne 
upon the clavate body of the polypes, where they are scattered irre- 
gularly among the tentacula. 
They are of a nearly spherical figure, and are attached to the 
polype by a short peduncle. 
The manubrium of the sac is large and simple,—- there are no 
radiating canals. 
In the female gonophores the ova are numerous, and may be seen 
in their young state to be each contained in a very delicate mem- 
braneous csecal tube of a pyriform shape, which closely embraces the 
ovum, and is attached by its narrow extremity, which constitutes a 
sort of neck to the base of the manubrium. The germinal vesicle 
and germinal spot are distinct. As the ova advance towards matu- 
rity, they appear to rupture the confining membraneous tube, and 
then lie free in the cavity of the gonophore. 
In the male gonophores, while they cannot be externally distin- 
guished from the female, the sporosac is filled with the spermato- 
genous cells. These may be seen, under slight compression, to be 
arranged in radiating lines, which, with a little careful examination, 
may be traced to the base of the manubrium. That these lines re- 
