CCELENTERATA. 
771 
seiits two distinct modifications of form — the plianerocodonic/’ which pre- 
sents the condition of a typically developed medusa, and is, in most cases, 
destined to enjoy a free locomotive existence, and the “ adelocodonic,” in 
which the medusa-form is more or less suppressed, and the gonophoie 
scarcely ever destined to become liberated from the trophosome. 
Among phanerocodonic forms the gonophore in Clavatella and Meutltej'ia 
is ambulatory instead of natatory ; and among adelocodonic forms we have 
a remarkable instance of a free locomotive gonophore in Dicoryne, where 
this body, often liberating itself from the trophosome, swims about by the 
aid of vibratile cilia. 
The mcdusiform zooid presents two types, which must be carefully distin- 
guished — the “ gonocheme,” in which the generative elements are produced 
in the walls of the manubrium, and the “ gonoblastocheme,” in which they 
are produced in special sacs developed on some part of the course of the ra- 
diating canals. The former he regards as truly sexual, while the latter is, 
properly sp('alnTig, non-sexunl and needs the development froni it of sexual 
buds for the formation of the gom'rativo olcnK'nls. Of the sexual form 
or gonocheme, examples are to be found in the medusa included by authors 
in the genus Sarsia, &c., while Thaumantias, Ohclia, &c., afford examples of 
the non-sexual form or gonoblastocheme. 
A comparison is instituted between the medusa and the sporosac or ade- 
locodonic gonophore, and it is shown that a strict parallelism may be traced ; 
while a similar parallelism is attempted to be demonstrated between the 
medusa and the polj^pite, in which it is mointained that the tentacles of 
the polypi ie have (heir homologues in the radiating canals of the medlisa — 
a view which the author believes to be supported not only by a comparison 
of structure and relations, but by the phenomena of development. 
Among special modifications of the gonosome, the author refers to the 
moniliform condition of the male gonophore in Eudcndrmm^ which he 
compares to a similar condition presented by the manubrium of the male of 
a /Sfifrsfa-like medusa captured on the Irish coast, as well as by the same 
part of the medusa referable to the genus Dipurmo,, M'Crady. 
To the capsular receptacle in which the gonophores are contained in 
such genera as Sertvlaria, Camiyctmdaria, &c., the term “ gonangium ” is ap- 
plied, and those hydroids which possess a gonangium are named angio- 
gonial,” while those in which the gonophores are not contained in an ex- 
ternal capsule are named “ gymnogonial.” 
In certain angiogonial genera the ova escape from the gonangium into an 
external receptacle which is situated on its summit. This is the “ acrocyst.” 
In most cases the acrocyst is destitute of any further covering ; but in certain 
species of Sertidarin.f S. rosacen and S. tainarisca, an additional covering is 
provided for it, so as to form a curious and complicated receptacle, in which 
the ova pass through certain stages of their development previously to being 
discharged into the surrounding water. 
In certain Plunmlaridm the gonangia are contained in groups within pe- 
culiar receptacles, to which the author gives the name of corbula,” and 
which he shows to be formed by certain ramuli of the trophosome which have 
undergone a metamorphosis, consisting in the suppression of the hydrothecse 
or so-called polype-cells, and the development on each side of numerous hol- 
low alternately placed leaflets. These leaflets curve round, and ultimately 
