210 THE VOYAGE OF H.M.S. CHALLENGER. 



Cirripathes propinqua. 



The type specimen of Cirripathes propinqua is not sufficiently well preserved to show 

 the general histological structure, but the muscular system is unusually well developed, 

 and the arrangement of the fibres has a closer resemblance to that of Actiniaria than has 

 yet been observed in any other Antipatharia. In the tentacles the ectoderm is about 

 0'06mm. in thickness, and the mesoglcea 0'03 mm. The entoderm is considerably folded, 

 and fills up the lumen of the tentacle. It varies in thickness from 29 to 87 jx. 

 Nematocysts occupy almost the whole surface of the tentacles, which are apparently 

 not folded or papillose. On the body-wall the nematocysts are not numerous, and 

 their place appears to be taken by elongate tapering epithelial cells (Stiitzzelleu). The 

 mesoglcea is apparently dentate on both its ectodermal and entodermal surfaces, and bears 

 on each side a well-developed row of muscular fibres, which follow the irregular outline 

 of the mesoglcea. The ectodermal layer of muscular fibres appears to be more than usually 

 developed in the curve by which the peristome passes into the body-wall. The entoder- 

 mal muscular layer has a greater development than that of any other species studied. 

 This is the only species in which undoubted muscular fibres have been observed in the 

 mesenteries. A sagittal section of a zooid, cutting the transverse mesenteries at right 

 angles, shows a delicate row of muscular fibres applied to each side of the mesogloea. 

 The mesoglcea is, however, not dentate as in other parts. Better preserved material is 

 necessary before one can decide whether there is any relation between the direction of the 

 muscular bands of the mesenteries in Cirripathes and those of other Zoantharia. 



The interzooidal areas bear a large number of slender mesoglceal ridges, clothed on 

 each side by entoderm, which have a direction chiefly transverse to that of the skeletal 

 axis. The appearance of these ridges in transverse section is shown in PI. XIV. fig. 

 7 se.<o. They vary considerably in length, the longest being situated at the lateral margins 

 ol each zooid. In the interzooidal regions (PI. XIV. fig. 7, c) the majority are very 

 short, but longer ones occur at irregular intervals. A delicate row of muscular fibres 

 is applied to the surface of the mesoglcea on each side. The floor of each zooid consists 

 of a delicate membrane, formed by a layer of mesoglcea, lined internally by entoderm and 

 externally by the axis epithelium. The cells of the latter are very irregular and some- 

 times columnar. The membrane is folded inwards towards the zooid at intervals, each 

 fold corresponding to the position of a spine. 



All the specimens examined have the ccelenteron almost completely filled with ova, 

 but the intermediate tissue is granular. In horizontal sections the ova are seen to be 

 contained in very large semicircular dilations of the transverse mesenteries. They also 

 fill up the lower portion of the lumen of the tentacles and extend more or less into the 

 interzooidal areas ; they sometimes, too, form relatively large rounded masses between 

 the interzooidal septa. 



