120 REPORT—1858. 
On laying open the female gonophore, the oval portion of it is seen to be occupied 
by a blastostyle, which gives origin to one or more sporosacs entirely resembling the 
male sporosacs except in the nature of their contents, which are here ova instead 
of spermatozoa. 
The oval portion of the gonophore terminates upwards by closing round the re- 
mote 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 
proper capsule of the gonophore, and is the only part developed in the male. From 
the summit of the blastostyle several irregularly-branched cecal tubes, apparently 
communicating with its cavity, are given off. They lie altogether external to the 
proper capsule, and embrace a delicate sac, within which are one or two ova in an 
advanced state of development, each in a delicate structureless sac of its own, which 
is continued by a narrow neck towards the summit of the proper capsule, with 
whose cavity it would seem to communicate; but the author did not succeed in 
tracing its connexions beyond this point. 
These ova, with their investing sacs, and the surrounding cecal tubes, would thus 
lie entirely exposed, were it not that they are surrounded by the three leaflets already 
mentioned as constituting the trihedral portion of the gonophore. These leaflets 
are given off from the oval portion or proper capsule near its summit, and being in 
contact by their edges, completely enclose a space which is occupied by the struc- 
tures just described. 
These structures are thus truly extra-capsular, and correspond with the extracap- 
sular ovigerous sacs which occur inSertularia pumila, S. cupressina, and other species, ~ 
and into which the ova are conveyed from the interior, to undergo, as in a sort of 
marsupium, a farther development previous to their final liberation as embryos. 
With regard to the true import of the sporosacs and their relation to the Medu- 
soid buds produced by other Hydroids, the author insisted on the necessity of bear- 
ing in mind that the spadix has no ectodermal covering, and consists of endoderm 
alone. He considered it to be homologous with the manubrium (‘“ peduncle”’) of a 
Medusa separated from its ectoderm by the intervention of the generative elements, 
which in the sporosac are always found between the entoderm and ectoderm of an 
organ strictly homologous with the so-called “peduncle” of a Medusa. By the 
continued growth of the generative elements, the ectoderm is separated more and 
more from the endoderm, which now constitutes a diverticulum from the cavity of 
the blastostyle, enveloped by the ova or spermatozoa; while the ectoderm forms the 
walls of a sac which immediately confines these elements. The whole is enclosed in 
an external sac, which seems to be an extension of the ectoderm of the blastostyle. 
We have thus, in the sporosac of Sertularia tamarisca, an organ which easily 
admits of comparison with the Medusoid buds of other Zoophytes ; it consists, in 
fact, of a manubrium peculiarly modified, so as to constitute a sac for the retention 
of the generative elements, and chiefly differs from the proper Medusoid buds in the 
non-development of a swimming organ or umbrella. In other instances (Cordylo- 
phora, &c.), as the author has elsewhere shown*, peculiar cecal tubes, generally 
more or less branched, are developed from the base of the spadix, and thence extend, 
along with the ova or spermatozoa, between the ectoderm and endoderm towards 
the summit of the sporosac. ‘The author had already compared these tubes to the 
radiating gastro-vascular canals of a Medusa; and if this comparison be just, they 
remain in the sporosac as the sole representatives of the parts found in the umbrella 
of a Medusat. A change of position, however, has taken place, and the radiating 
canals, having withdrawn themselves from the covering of ectoderm which they pos- 
sess when forming a constituent part of the developed umbrella, are now composed 
of endoderm alone, and lie between the endoderm and ectoderm of the manubrium, 
where they form cecal processes from the spadix or endodermal portion of the ma- 
nubrium, 
* Phil. Trans. 1853. - 
t In a paper by the author on Cordylophora lacustris (Phil. Trans. 1853), he expressed his 
belief that the umbrella of a Medusa had its representative in the walls of the sporosac; 
subsequent examination, however, of the sporosacs in a great number of species had caused 
him to modify this view and adopt that contained in the present communication. 
