the anatomy of the madreporaria. 11 



has so shrunk on to the corallum that the costse project through it, 

 and the exact conditions are difficult to determine with certainty. 



B. Anatomy. — The general anatomy of the colony, as regards the 

 relations of canals, body wall, polyp cavities, &c, agrees with that 

 of M. Durvillei. Beyond the fact that in M. aspera the polyp cavities 

 are placed closer together, and that therefore there are fewer canals 

 in the corallum, there is little or no difference between them. As 

 regards the polyps, however, there is no dimorphism; all the polyps, 

 except those which are obviously immature buds, are identical in 

 structure. 



A typical polyp possesses twelve perfectly normal mesenteries, and 

 a stomatodteum which is a simple invagination of the external body 

 wall. When numbered on the same system as in M. Durvillei, it is 

 found that those mesenteries marked 1, 2, 4, 6, 7, 9, 11, 12, are the 

 ones which develop mesenterial filaments, that is, the same mesen- 

 teries as in M. Durvillei, with the addition of the abaxial " directives ;" 

 while the others, 3, 5, 8, 10, generally have no filament, and do not 

 extend to the bottom of the stomatodseum. 



The apical polyps are about twice the size of the others, but, 

 except for their possession of more septa, are identical in structure 

 with them. 



The muscles in both apical and lateral polyps are arranged on the 

 mesenteries just as in Actinia, and present nothing unusual in 

 structure. 



Tentacles I was unable to recognise, macroscopically or by sections, 

 but a figure by Dana shows that they are present, and twelve in 

 number. In this, as in the species last described, they have shrunk 

 into insignificance, owing to the action of the spirit in which the 

 specimens were preserved. They agree with M. variabilis, in which, 

 according to von Koch, they are also exocoelic and entocoelic. 



The histology calls for no remark, agreeing with that of forms 

 already described. Calycoblasts were very distinctly present in the 

 growing parts of the colony. 



0. Method of Buddin*;. — With regard to this, I have been able 

 to glean but little information ; since the immature polyps are so 

 crowded with zooxanthellae, owing presumably to the amount of 

 nutriment supplied to them, that the tissues are much obscured. 



The stomatodyjum is invaginatcd to a considerable depth into the 



