492 
SEITARO GOTO 
of this species than in H. sodahs. These show that in the thinner 
part of the shell its hard parts consist of two parallel chitinous 
lamellae about 7-22/^ in thickness and 0.1 mm. apart, connected 
together at many points by strong chitinous trabeculse of varying 
thickness (fig. 20). It was probably these trabeculse that Inaba 
mistook for surface spines. The inner surface of the shell is bounded 
by the inner of the two lamellae just mentioned; the outer surface 
is also largely bounded by the outer of the two lamellae, but in 
many places chitinous tubes of the structure generally seen in 
monosiphonic hydroids take rise from the outer lamella and 
creep about on the outer surface of the shell in close apposition 
to the former. The interspaces between the two chitinous lamellae 
are completely filled with ectoderm which contains numerous 
ramifying endodermal tubes forming a network, to which is due 
the appearance of the inner surface of the shell mentioned above. 
The superficial tubes above referred to are filled with the continua- 
tions of the endoderm and ectoderm filling the interlamellar 
cavities, exactly as in monosiphonic hydroids; but I have never 
seen them give rise to polyps, although my observations on this 
point are confessedly incomplete. As to the thicker part of the 
shell, I have not been able to obtain satisfactory serial sections 
owing to the presence of much dirt and sand grains. Where the 
chitin is of some thickness in any part of the shell it is seen to be 
composed of several superposed layers. According to my obser- 
vations there is no coenosarc on the surface of the shell, and the 
relations of the soft part and the chitin are in this species nearer 
those found in the typical hydroids than in H. sodalis. 
In this as in the preceding species there is always a small gas- 
tropod shell in the apex of the hydroid skeleton ; in one case it was 
that of a species of Fusidae only 6.5 mm. long, although the hydroid 
shell was 25 mm. in length. It is interesting to note that this 
species never grows so large as the preceding, although found 
in the same localities. The mother whorl of the hydroid shell is 
r.elatively very large and the turret very small. 
So far as I have observed, the polyps are of two kinds, nutri- 
tive and reproductive. The former, or gasterozooids, may be found 
in any part of the colony, but most frequently they are especially 
