10 G. HERBERT FOWLER. 



It is interesting to note that in M. Durvillei, as in Alcyonaria and 

 Antipatharia, two mesenteries are distinguished from the rest by 

 running far deeper into the corallum or rachis. This may be a 

 specialisation for circulatoiy purposes, as has been shown by Dr .Wilson 

 to be true for certain Alcyonaria, or connected with production of 

 the generative elements, as in the case in Antipatharia ; in M. 

 Durvillei certainly the latter, perhaps also the former, holds good. 



Madrepora aspera (Dana). 



For a fragment of this coral, fortunately the upper part of a 

 branch, I am again indebted to Professor Moseley. 



The species was founded by Dana (7), who gives a good figure of 

 the colony. 



A. Corallum. — A transverse section of the corallum (Fig. 10) 

 shows that the polyp cavities (a a') are arranged in a definite ring, 

 and not merely confined to three sides as in M. Durvillei, round a 

 central cavity into which project six septa, more or less fused 

 together at their free edges. This central cavity (c.c.) is continuous 

 with that of the apical polyp of the branch. The arrangement of 

 the internal longitudinal canals is not so definitely concentric as in 

 M. Durvillei, but the method of circumferential growth of the 

 corallum appears to be similar in both species, since the costae appear 

 to fuse over the external longitudinal canals. (Vide Fig. 10, x, and 

 p. 3). 



In the apical polyps are found six distinct entocoelic septa, and 

 six smaller exocoelic, of which all are not always present ; in the 

 others generally only an axial or abaxial septum. A similar differ- 

 ence between them was observed by von Koch (8) in M. variabilis, 

 where both exosepta and entosepta were present in the apical polyps, 

 but entosepta only in the rest. 



In this form, as in the former species, there appears to be no 

 relation in number and position between costse and septa, the former 

 being by far the most numerous. 



The costce are apparently formed as in M. Durvillei, that is, at the 

 points where the endoderm and mesoderm apposed to the exterior 

 surface of the corallum touch the external body wall (vide p. 4 and 

 Fig. 4), but in both species, owing to alcoholic contraction, the latter 



