OF COENOPSAMMIA FROM LIFtJ. 373 



No trace of a definite nervous layer can usually be distinguished, except at the 

 attachment of the mesenteries to the body wall under the tentacles, where it is some- 

 times well marked with numerous small round nuclei. 



The great mesenteric retractor muscles (Fig. 21) are situated on simple or branched 

 lamelliform folds of the structureless membrane. They consist of separate long fibres, 

 rectangular or oval in transverse section, and stain very deeply and uniformly with 

 Heidenhain's iron haemato.xylin. Each fibre runs from the mouth-disc to its insertion 

 along the line of the attachment of the mesenteries as shown in Figure II. At each 

 end the fibres bi'eak up into a number of small fibrils, which spread out and appear 

 to be attached to the structureless membrane without any connection with the endoderm 

 epithelium. At the attachment of the mesenteries to the corallum some of these 

 fibrils run directly into the structureless membrane, and I would suggest that the fibres, 

 previously described in this position, are really the attaching fibrils of these muscles. 



The circular rrtuscle — Rotteken's muscle — consists of similar but much smaller fibres 

 (Fig. 5), the attachment and course of which I have, however, been unable to satis- 

 factorily determine. 



On the sides of the mesenteries opposite to the great retractor muscles, I have 

 been unable to distinguish any similar muscular fibres running transversely to the long 

 axis of the polyp — any protractor fibres in fact. In sections numerous small muscular 

 processes are cut across, but these are quite short, and are basal processes of the 

 endodermal epithelium. Further, they do not seem to run markedly more transversely 

 than longitudinally. As the polyp is very closely attached to the corallum, they 

 could not either have any powerful protractor action, and it seems to me that the 

 expansion of the polyps must be brought about by other means. 



Generative Organs. I have not been able to trace the inwandering of the 

 genei-ative cells from the endoderm into the structureless membrane, but there is little 

 doubt that it occurs in the same way as the Hertwigs have described in the Actiniaria 

 (14 and 15). The endoderm round each ovum is very much thickened, and in the 

 contracted condition of the polyp the coelenterou between the mesenteries is almost 

 completely obliterated (Fig. 22). No cell outlines can be distinguished, but the endoderm 

 appears to be a very elongated and much vacuolated epithelium of a columnar facies. 

 The nuclei, which are small and not very distinct, are situated towards the free side of 

 the epithelium, which is very granular. Near the base of the epithelium a few granules 

 are found, which in places appear to be passing into the ova, large granules bemg 

 constantly seen situated partially in the ova and partially in the endoderm. 



The structureless membrane completely surrounds each ovum as a very thin layer 

 and the membrane connecting it with the general structureless membrane of the 

 mesentery is exceedingly fine. It can usually be distinguished, however, by the well 

 marked basal muscular processes of the endoderm, which are not generally found over 

 the ova. I have not found any definite " Fadcnapparat " as described by the Hertwigs 

 in Actiniaria, nor is there any trace of any of the ova serving for food to the rest. 



The ova vary up to -45 mm. in diameter and are full of yolk spherules and 

 granules. The nucleus is a large centrally situated body with a homogeneous deeply 

 staining round nucleolus. No definite nuclear membrane can be distinguished. Towards 



W. IV. ^^ 



