584 
G. HERBERT FOWLER. 
and “ventral” halves is clearly distinguishable in both soft 
tissues and corallum. Two of the septa are very rudimentary, 
and both this fact and the absence of mesenterial filaments on 
ten of the mesenteries would seem to indicate a degeneration, 
of which I hope to bring forward a second instance in a future 
paper. Between the polyps runs a similar canal system to 
that already described by v. Koch in Stylophora. The anatomy 
of Pocillopora, so far as mentioned, appears to agree in all 
respects with that of Seriatopora, and the polyps exhibit the 
same marked orientation. 
Moseley (11) has also described the macroscopic anatomy 
of three other Madreporarian polyps. His observations on 
Flabellum are mostly incorporated with my own below, and 
need not therefore be recapitulated here; and of Stephano- 
phyllia I hope to give a detailed description in a future 
paper. 
Of Bathyactis, which is planoconvex in shape, the plane 
being the basal surface, he records that on decalcification a 
lamina of ectoderm and mesoderm separates off from the base. 
This fact, together with its shape, suggests that the original 
basal ectoderm of the embryo persists in this species through- 
out life, in its primitive position, except for such part as grows 
up with the skeleton (the calycoblasts). 
To sum up the undoubted facts elucidated by these observers : 
1. The adult Madreporarian polyp is built distinctly on the 
Actinian type, except for the absence of an external body- 
wall in some cases (Caryophyllia, Cladocora), which is then 
replaced physiologically by the imperforate theca. 
2. The corallum is a product of the ectoderm, and deposited 
outside the embryo. 
3. This ectoderm persists in the adult as the layer of 
calycoblasts, to which the continual growth of the corallum 
is attributable; thus the skeleton is morphologically ex- 
ternal to the polyp throughout life. 
4. Between this layer and the cavity of the coelenteron, and 
clothing every part of the skeleton, is a layer of mesoderm and 
endoderm, forming the internal body wall. 
