52 
tute of its investing capsule, and then presents merely the condition 
of a naked blastostyle with its sporosacs (or medusae ]). 
The medusae, like the gymnophthalmse generally, consist of an 
umbrella or mantle with radiating and circular canals, and with a 
central projecting organ, in which the stomach is excavated, and 
which carries the mouth at its extremity. To this central organ 
the term peduncle has commonly been given, a name which conveys 
a wrong idea as suggestive of an organ of attachment and support. 
It is also frequently called the stomach, a term also obviously in° 
correct, as the true stomach may really occupy but a small portion 
of the entire organ, Huxley,* seizing, as the author thinks, upon 
its true significance, names it polype, but as it will be more conve- 
nient in the present investigations to distinguish it from the ordi- 
nary nutritive polype of the colony, it is proposed to speak of it 
under the name of manubrium , a term suggested by its position 
with regard to the mantle being such as to admit of a comparison 
with that of the handle of an umbrella. 
The sporosacs consist of parts which have their strict homologues 
in the medusse. These parts will therefore be spoken of under the 
same names as those of their equivalents in the medusse. 
These preliminary remarks will render easily intelligible the new 
terms which, after much consideration, the author deemed it neces- 
sary to introduce, as the only way by which cumbrous circumlocu- 
tion can be avoided and precision given to our descriptions ; and he 
proceeded in the next place to describe the structure of the repro- 
ductive system in certain species which have in this respect either 
never received, so far as he is aware, the attention of the compara- 
tive anatomist, or which, though studied to a certain extent, still 
present certain points worthy of attention, but which have hitherto 
escaped notice. 
Hydractinia echinata. 
In Hydractinia echinata the gonophores are borne upon certain 
polypes, which, as is well known, are destitute of tentacles and mouth, 
and differ also in some other respects from the other digestive poly- 
pes of the colony .+ The gonophores surround the naked stems of 
* Lectures on General Natural History in Medical Times. 
t I have observed in these generative polypes an oval mass nearly filling the 
cavity of the body. It is developed from the endoderm, and projects from the 
floor of the cavity. It reminds one of the manubrium of a sporocyst, but is 
apparently solid. 
