374 
REPORT—1863. 
The trihedral portion, with its pyramidal summit, is formed of three 
leaflets (b), which merely touch one another by their edges without adhering, 
so that they may be easily separated by the 
dissecting-needle or by the embryo during 
its escape. They consist of the same chi- 
tinous material as that which forms the 
rest of the gonangium, excreted doubtless 
originally upon the surface of an ectodermal 
lamina. 
On laying open the gonangium, the oval 
or proximal portion of it is seen to be oc- 
cupied by a blastostyle (c,d), which gives 
origin to one or more gonophores (¢). It 
terminates upwards by closing round the 
distal extremity of the blastostyle, where 
it forms a ring, with tooth-like processes, 
by which the extremity of the blastostyle is 
encircled. This oval portion constitutes the 
gonangium proper, and is the only part de- 
veloped in the male. 
From the summit of the blastostyle 
several irregularly branched cecal tubes (7), 
apparently communicating with its cavity, 
are given off; they lie altogether external 
to the oval portion or gonangium proper,and 
embrace a delicate sac (/), within which are 
one or two ova (/) in an advanced stage of 
development, each in a delicate structureless 
sac (m) of its own, which is continued by a 
narrow neck to the summitof theblastostyle. 
The ova, with their investing sacs and 
the surrounding cecal tubes, are further 
closed in by the three leaflets already men- 
tioned as constituting the trihedral portion 
of the gonangium. These leaflets are given 
off from the sides of the oval portion, or 
proper gonangium, a little below its sum- 
mit; and, being in contact by their edges, 
completely enclose a space which is occupied 
by the structures just described. 
The homological relations between the 
marsupial receptacles of Sertularia rosacca 
and S. tamarisca are at once apparent, 
and .are very interesting. The ramified 
tubes (fig. 112) of S. tamarisca are mani- 
festly the representatives of the eight sim- 
ple tubes (fig. 10 2) in S. rosacea, while the 
three broad chitinous leafletswhichsurround 
the whole externally are homologous with 
the continuation of the gonangium in 8S. 
Fig. 11.—Female gonangium 
with marsupial chamber of 
Sertularia tamarisca. 
a, lateral walls of the gonangium 
proper ; 4, two of the three chitinous 
leaflets which form the outer walls of 
the trihedral marsupial chamber ; ¢, 
blastostyle ; d, opercular summit of 
blastostyle ; e, gonophore budding 
from the blastostyle ; Jf, its ectotheca ; 
g, its endotheca ; 2, ova; 7, ramified 
ceecal processes from thesummit of the 
blastostyle ; 4, delicate membranous 
sac, forming the inner walls of the 
marsupial chamber ; /, ova contained 
within this sac ; the germinal vesicle 
has disappeared, and they have nearly 
acquired the condition of planule ; 
m, delicate special sac of the ovum. 
rosacea, where, with its prominent ridges and spines, it forms an external 
capsule-like covering for the sac into which, as in S. tamarisca, the ova are 
expelled from the gonangium proper. 
