IÇJI5-] Fauna of the Chilka Lake : Coelenterates. 81 



difficult to demonstrate on the preserved specimen, are conspicuous in the living 

 animal. They are confined to a region separated by a short imperforate "neck" 

 from the disk and otherwise occupy approximately the anterior fifth of the ex- 

 panded column. They have thin but sometimes rather prominent lips and run 

 across from mesentery to mesentery, but only in the spaces separating complete 

 mesenteries and not always in these. Their arrangement is irregular, but their 

 relation to the mesenteries renders it necessary for them to form vertical rows, 

 which contain from 3 to 7 cinclides each. When the apertures are closed they have 

 the appearance, in the living animal, of fine white transverse lines bridging the 

 mesenterial spaces into which they open (pi. viia, fig. 3a). 



The stomodaeum extends when expanded for about one-third the length of the 

 expanded column, but can contract independently of the body as a whole. Its walls 

 are not very thick, but the endoderm forms a series of distinct ridges. Transversely, 

 in the sulco-sulcular axis, it is relatively wide, occupying by far the greater part of 

 the diameter of the column; it is, however, strongly compressed. 



There are as a rule twelve imperfect, infertile mesenteries as well as the twelve 

 complete ones. Sometimes all of the latter bear filaments and gonads, but in some 

 individuals not more than one-half or two-thirds do so ; the incomplete mesenteries are 

 almost vestigial. Owing to the great width of the stomodaeum the directive mesenteries 

 are relatively very short. The basilar muscles are small and feeble and the muscle- 

 banners fairly strongly developed. On the directive mesenteries the latter have in 

 some cases a narrow, elongate form in cross-section, while in others they are 

 shorter and distinctly kidney-shaped. Most mesenteries have a stoma, but this aper- 

 ture is sometimes absent and when present varies greatly in size, shape and posi- 

 tion. As a rule it is very large, of a broad transverse or oblique oval or ovoid form 

 and distinctly internal in position ; but sometimes it is much reduced in size and 

 situated nearer the column- wall than the stomodaeum. I have seen one mesentery 

 in which not only was the stoma, which was external in position, very large, 

 but the whole of the membrane between the muscle-banner and the body-wall reduced 

 to a narrow band by a great gap or emargination in the lower part of the mesentery. 

 The band was bounded above by the stoma and below by this gap. 



As a rule acontia, which are never well developed, are only present on a few of 

 the mesenterial filaments. The upper trilobed portion of the filaments is short — as 

 a rule shorter than the stomodaeum, and the simple portion relatively long; but the 

 proportionate length of the different parts of the filaments varies greatly even in the 

 mesenteries of a single individual. 



The gonads are normal in structure, and as far as I can ascertain the animal is 

 dioecious. 



The anterior sphincter is even less differentiated than in M. schillerianum , but 

 in carefully preserved expanded specimens which have been rendered transparent, a 

 few folds of the muscle-sheath can be detected in the region occupied by the cin- 

 clides. These folds lie in the mesogloea at the base of the endoderm and are not 

 accompanied by any independent muscle-spaces. The rest of the muscle-sheath 



