388 REPORT—18638. 
female stems are united by the creeping stolon into a common colony. In 
Hydractinia, on the other hand, whose habit is entirely similar to that of 
Dicoryne, we never meet with the two sexes in a common colony; perhaps 
even never investing the same shell. 
As a general rule, there is no perceptible difference between the male and 
female colonies of the same species, either in the trophosome or the gonosome, 
beyond what is, of course, presented by the generative elements themselves. 
In some cases, however, the difference is sufficiently well marked. Thus in 
Sertularia tamarisca the male and female gonangia differ strikingly from one 
another; for the male gonangia are compressed, somewhat obcordate recep- 
tacles with a short terminal tubular aperture; while the female are oval for 
about the proximal half of their height, and then become trihedral with the 
sides diverging upwards, the whole being terminated by a three-sided pyramid 
whose edges are cut into two or three short teeth, and the basal angles pro- 
longed into a short spine*. 
So also in Sertularia rosacea a well-marked difference may be seen. The 
male gonangia are here of a conical form, curved near the apex, which is 
their point of attachment, and provided with six longitudinal ridges in the 
form of thin projecting lamelle, each of which terminates at the distal 
extremity in a free pointed process which arches over the summit of the 
gonangium. In the female gonangium the longitudinal ridges are eight in 
number, while two opposite ones being greatly more developed than the others" 
give to the gonangium the very elegant and striking form which caused Ellis 
to compare it to a “lily or pomegranate-flower just opening.” The female 
gonangium of both Sertularia rosacea and S, tamarisca differs still further 
from the male by the remarkable marsupial chamber which I have already 
described as developed within it. f 
It will also be borne in mind that, in those species which develope an 
acrocyst on the summit of the gonangium, this body is formed only in the 
female; while it is on the female gonangium alone of Haleciwm halecinum 
that the little geminate polypite already described is produced; and to 
these cases we may also add the difference presented by the male and female 
meconidia in Laomedea Lovéni. 
Among the gymnogonial Hydroida also, certain differences may be occa- 
sionally observed between the male and female. Thus in certain Tubularie, 
the tentaculoid tubercles which crown the gonophore are more fully deve- 
loped in the female than in the male; but the most striking difference is 
found in the genus Eudendriwm, whose male gonophores are situated in a 
verticil on the body of the polypite, and present the remarkable polythalamic 
condition already described, while the female gonophores originate irregularly 
for some distance backwards on the branch, and are always monothalamic. 
This difference between the male and female gonophores in Hudendrium 
struck Cavolini long before the presence of a male element in the Hyprorpa 
was suspected, and led him to suppose that Hudendriwm reproduced itself by 
two different kinds of eggs. In accordance with this view, he called the 
female gonophores in his Sertularia (Eudendrium) racemosa, “ nova aracemo,” 
and the male gonophores ‘‘ uova a corimbo”’+. 
The differences above described between the male and female are all con- 
fined to the gonosome ; the trophosome, however, does not appear to be always 
exempt from a participation in sexual difference, for in Hydractinia polyclina, 
* It is apparently the male gonangia which Ellis has figured in his description of this 
species. 
+ Cavolini, Mem. Polypi Marini, 1785. 
