ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 381 
I have thus far endeavoured to give a complete account of the morphology 
of those portions of the hydroid which are destined for the origination and 
protection of the generative elements; but, before passing to the considera- 
tion of these elements themselves, it may be well to inquire whether there 
is any general rule as to the distribution of the adelocodonic and phanero- 
codonic gonophores, and of the two forms of the latter among the several 
families of the Hyprorpa. 
There is no established instance of the same species of hydroid producing 
both phanerocodonic and adelocodonic gonophores either simultaneously or 
consecutively. Sars is certainly in error when he includes under his Podo- 
coryne carnea two forms of hydroids, one with developed meduse, and the 
other with sporosacs*; and there can be little doubt that Van Beneden has 
made some confusion between two distinct species when he figures a portion 
of a hydroid colony, which he names Campanularia geniculata, with two kinds 
of gonangia, one containing meduse, and the other sporosacs +. 
The Tubularida present examples of both phanerocodonic and adelocodonic 
gonophores, which are borne either by the trophosome directly or by gono- 
blastidia ; but, so far as our present knowledge extends, the instances of 
adelocodonic gonophores .are rather more numerous among the Tubularida 
than those of phanerocodonic gonophores. The phanerocodonic gonophores 
of the Tubularida belong, so far as we yet know, exclusively to the type 
described above under the name of gonocheme, the generative elements 
not being here proved ever to originate in special buds upon the course 
of the radiating canals. I regard it, however, as highly probable that the 
sexual lobes of Nemopsis, whose bases extend over portions both of the 
manubrium and radiating canals, will prove to be true zooids. The tro- 
phosome of Nemopsis has been shown by M°Crady to be a free Tubularian 
polypite; and if the zooidal nature of the sexual lobes be proved, we shall 
have among the Tubularida an exceptional condition which may be compared 
to that presented by Laomedea tenuis among the Campanularians ¢. 
the author reeognizes in the corbule of Aglaophenia pluma, and some other allied species, 
their true significance as metamorphosed branches. He mistakes, however, the nature of 
the metamorphosis, while, in accordance with the prevailing view, he sees in the receptacles 
a question bodies in all respects corresponding to the proper gonangia of the other 
ydroids. 
Forbes, moreover, extends his generalization, applying it to the gonangia of the other 
Sertularians, which he believes must be all regarded as peculiarly metamorphosed branches, 
with metamorphosed and confluent hydrothecz, exactly in the same way that the floral 
verticils in plants may be referred to verticillate, metamorphosed, and variously combined 
leaves. ‘The vesicle,” he says, ‘‘is formed from a branch or pinna through an arrest of 
individual development, by a shortening of the spiral axis, and, by a transformation of the 
stomachs (individuals) into an ovigerous placenta, the dermato-skeletons (or cells) uniting 
to form a protecting capsule or germen ; which metamorphosis is exactly comparable with 
that which occurs in the reproductive organs of flowering plants, in which the floral bud 
(normally a branch clothed with spirally arranged leaves) is constituted through the con- 
traction of the axis and the whorling of the (individual) appendages borne on that axis, 
and by their transformation into the several parts of the flower (reproductive organs).” 
The theory, however, involved in the above statement, attractive though it be, is con- 
tradicted by the actual development of the parts in question. When Forbes wrote, so 
little was known of the structure and development of the Hyproma, that this accomplished 
and lamented naturalist may well be excused if some parts of his very suggestive paper 
have refused to stand the test of subsequent research. 
* Sars, Faun. Lit. Norv. p. 7. pl. 2. fig. 5. 
t Van Beneden, Mém. sur les Campanulaires, pl. 3. figs. 1-6. 
} Agassiz describes (Cont. to the Nat. Hist. of the United States, vol. iv. p. 281) the me- 
dusa of his Pennaria gibbosa as presenting slight fusiform enlargements of the radiating 
canals, which he is disposed to regard (though not without doubt’) as rudimental generative 
