REPORT ON THE ANTIPATHARIA. 193 



distance beneath the surface such sections show ten mesenteries, arranged in a similar 

 manner to those of Cirripathes propinqua (cf. fig. 4, p. 39). Each mesentery 

 consists of a thin layer of mesoglcea, clothed on each side by entoderm. The mesoglcea 

 of the stomodaeuru is thus united to that of the oral cone by ten slender partitions, and 

 the interseptal chambers thus formed are lined by entoderm. The interseptal chambers 

 are at first very small, and those at each end of the long axis of the stoinodaeum 

 remain slit-like for a considerable distance. The "directive" mesenteries are very narrow 

 for their whole course (cf. PI. XIII. fig. 7) ; beneath the stomodseum they are attached 

 to the body -wall for a very short distance, and have a slightly thickened border. The 

 transverse pair of mesenteries increase in breadth in the lower part of the oral cone, 

 and beneath it rapidly extend to the lateral extremities of the polyp. In their lower 

 section these mesenteries are much thickened and bear the sexual elements. The 

 greater part of the lateral sections of the ccelenteron is occupied by the transverse 

 mesenteries and by the convoluted filaments to which they give rise. They are the 

 longest and most important of all the mesenteries, and their filaments practically fill up 

 the whole of the space beneath the stomodseum. The two pairs of secondary mesenteries, 

 situated one on each side of the transverse mesenteries, are never important, and become 

 lost before the base of the stoniodaeum is reached. In the subhorizontal section figured 

 (PI. XIII. fig. 7), the member of each secondary pair which is situated above the 

 stomodseuni extends from the stomodseum to the body-wall. On the opposite side of 

 the stomodseum the right hand mesentery is seen to have lost its connection with the 

 body- wall, but remains as a projection from the stomodseum. That on the left hand 

 has disappeared above the level of the section in that part. The secondary mesenteries 

 do not bear filaments, nor is their free margin thickened, as in the case of the "directive" 

 mesenteries. The appearance and situation of the mesenterial filaments will be under- 

 stood by a reference to the figures already cited ; their structure will be described later. 

 The relation of a polyp to the sclerenchyma, which serves as its support, is best studied 

 in sagittal sections showing the sclerenchyma in transverse section. PI. XIII. fig. 

 6 represents a section passing through the extreme elongation of the stomodseum, and 

 shows the insertion of the sagittal tentacles. Beneath the stomodseum the section 

 passes through two mesenterial filaments, and still lower, quite at the base of the 

 ccelenteron, a rounded mass of tissue is seen, containing a central lumen, within which 

 the sclerenchyma is situated. The sclerenchymatous sheath consists externally of a 

 comparatively thick and irregular layer of entoderm, beneath which is a thin layer of 

 mesoglcea. Its inner surface is clothed by a thin and irregular epithelium, which con- 

 stitutes the secretory layer. The sclerenchyma consists of a large number of very thin, 

 concentric, horny lamellse, arranged around a comparatively large central lumen. The 

 mesoglcea of the sclerenchymatous sheath is united to that of the base (ccenenchynia) by 

 means of a short septum (PI. XIII. fig. 6, sep.'), which runs the whole length of a branch. 



(ZOOL. CHALL. EXP. — PART LXXX. — 1889.) Llll 25 



