EEPORT ON THE HYDROIDA. 



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). 



Hydrothecce. — In all the Plumularidae hydrothecse are borne on special ramuli, 

 which are usually disposed in pinnae, and for which the convenient term hydrocladium , 

 as proposed by Ku'chenpauer, may be adopted. In a few species (PI. IV. figs. 3, 4) hydro- 

 thecae 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. 



Fig. 1.— Longitudinal section of the polysiplionio stem of Aglaopheiiia coarctata, showing the hiteral offsets 

 through which the component tuhes 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 XVII.). 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 surfiice of the waUs 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 (Pis. XV. and XVIII. ). This, however, is only the optical expression of a fold 

 in the walls of the hydrotheca. 



1 The exception here referred to is found in an Eleutheroplean Plumularidan not yet described. 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 Literal tooth on eacli side. 



