REPORT ON THE HYDROIDA. 5 
the component tubes, those of two juxtaposed tubes meeting one another and inosculating 
in such a way as to suggest the conjugation of a Zygnema (fig. 1). 
Hydrothece —In all the Plumularide hydrothecee are borne on special ramuli, 
which are usually disposed in pinne, and for which the convenient term hydrocladium, 
as proposed by Kirchenpauer, may be adopted. Ina few species (PI. IV. figs. 3, 4) hydro- 
thecze are also carried directly by the stem. 
In the Eleutheroplea the margin of the hydrotheca is, with, so far as I know, only 
one exception,’ invariably destitute of all trace of serration. The peculiar ridge which 
I have termed the “ intrathecal ridge,” and which constitutes a characteristic feature in 
the Statoplea, is never present in the Eleutheroplea. 
Fic. 1.—Longitudinal section of the polysiphonic stem of Aglaophenia coarctata, showing the lateral offsets 
through which the component tubes communicate with each other. 
In the Statoplea the margin of the hydrotheca is in most instances deeply serrated 
(Pl. XL, &c.). In a few it presents only an indistinct crenation (Pl. XIV.), while in a 
few it is quite entire (Pl. XVIL). In almost every case there is present in the 
hydrotheca of the Statoplea a slightly projecting chitinous ridge (Pl. XL, &c.), which 
runs on the inner surface of the walls transversely from behind forwards, but with a more 
or less oblique direction, and which more or less completely encircles the cavity of the 
hydrotheca, thus forming an imperfect septum, which divides the hydrotheca into a 
proximal and a distal portion. This is the intrathecal ridge, which, as just said, is never 
present in the Eleutheroplea. In some species of Statoplea, what has the appearance of a 
similar ridge running from before backwards may be seen in the anterior portion of the 
hydrotheca (Pls. XV. and XVIII.). This, however, is only the optical expression of a fold 
in the walls of the hydrotheca. 
1The exception here referred to is found in an Eleutheroplean Plumularidan not yet deseribed. For an 
opportunity of examining it I am indebted to Miss Gatty. Among other very exceptional characters, the margin of 
the hydrotheca is here provided with a strong anterior mesial tooth, and with a strong lateral tooth on each side. 
