THE ANATOMY OF THE MADREPORARIA. 245 



as will be seen by the figures, the outermost ends of the septa 

 (PL XI, a, b). 



Further, the mesenteries and chambers between them appeared to 

 be continued into this external part of the polyp. These appearances 

 he explained by supposing that, as the peripheral ends of the septa 

 approximated and fused, they surrounded the mesenteries, dividing 

 them ultimately into a central and a peripheral part. As a further 

 proof he adduced the observation that in microscopic sections of the 

 corallum sutures were visible in the theca at the points where he 

 supposed the septa to have fused. 



I venture to think with Moseley (5) that this explanation is erroneous; 

 that the appearances in the first section (PL XI, a) are due merely 

 to the fact that in this, as in many corals, the secretion of calcium 

 carbonate is most active about the septa, which consequently rise 

 slightly above the level of the theca, as may be seen in any figure of 

 Caryophyllia ; and further that, in the second section (PL XI, b), the 

 apparent continuation of the mesenteries and chambers between them 

 over the lip of the calyx is not due to their having been cut into two 

 portions by fusion of the septa, but to more or less abnormal contrac- 

 tion due to the use of alcohol ; in life the polyp, when fully expanded, 

 undoubtedly stretches over the lip, but in these forms, so far as I can 

 ascertain, in natural contraction it is completely within the calyx. 

 Further, as appears from his own researches and those of others on 

 different forms, the whole skeleton, instead of being, as he describes, 

 free in the coelenteron, is shut off from it by a layer of endoderm and 

 mesoderm, and as much outside it as the rest of the corallum ; these 

 layers he himself figures as clothing another part of the septum, 

 though of this portion no histological details are given. Von Heider, 

 in a paper shortly to be referred to, states that Von Koch has over- 

 looked the fact that the whole of the corallum is covered externally by 

 ectoderm and mesoderm ; certainly this form requires more complete 

 investigation. Again, having ground many microscopic sections of 

 corals, I can afford no credence to "sutures;" in the process cracks 

 fly through the coral in all directions. But if evidence of a directly 

 contrary character is needed, the case of Flabellum may be adduced, 

 in which (5), according to Moseley, sutures run not between the fused 

 ends of the septa — i.e. through the theca — but down the centre of 

 each septum. 



