14 GENERAL REMARKS. 
one, and the corallites of M. hebes agree in form with those of M. millepora, M. prostrata, &e., 
and not with M. cytherea and allied forms. The absence of M. corymbosa from Dana’s list 
will also be noted. Doubt has already been cast on Dana’s identification of M. corymbosa, 
Lamk. ; and the fact that he did not associate M. corymbosa, Dana, with M. cytherea in the 
list quoted lends further support to the view that Dana’s species is not identical with that of 
Lamarck. 
Whether the radial polyps of M. aspera, which have equal tentacles according to Dana’s 
figure, differ structurally from those of M. prostrata is not at present known. The account 
given by Fowler of the structure of M. aspera probably refers to the species M. pocillifera, 
which is, however, closely allied, and is here regarded as a member of the same group. 
A fragment of the material has been kindly placed at my service by Dr. Fowler, and I find 
that it agrees closely with the ‘Challenger’ specimens of M. pocillifera. The only other 
species studied by Dr. Fowler does not belong to the same group as M. prostrata, so that we 
have at present no means of comparison. It appears, however, probable that certain types of 
arrangement of the septa are associated with morphological differences in the polyps which 
produce them; and a fuller knowledge of the structure of the soft parts will doubtless supply 
valuable data for the purpose of classification. I may, however, point out that for this 
purpose it is not sufficient to indicate general structure ; it will be necessary to give details 
for the axial corallites, for the prominent radial corallites, and also for the immersed or other 
forms which may differ from the usual type. 
Structure of the Polyps, and the Relation of Soft Tissues to the Skeleton—Fowler * has 
studied the anatomy of two ‘ Challenger’ species of Madrepora, in one of which a new and 
interesting type of dimorphism occurs. The present section consists of a summary of his 
results, together with a few supplementary observations of my own. 
The external body-wall consists of the usual three layers—ectoderm, mesoglea, and 
entoderm,—and is supported on echinulations or rugze both on the radial corallite-walls and 
in the inter-corallite regions, where the latter are of sufficient importance to possess inde- 
pendent supports. Under the external body-wall and between the ruge (M. pocillifera) 
a series of external longitudinal canals exist, which open into each other and also through the 
corallum into a series of internal canals with radial and transverse connections; these, in 
turn, communicate with the general ccelentera of the polyps, and all communicate eventually 
with the ccelenteron of the axial polyp. These canals occupy the channels in the corallum 
already described. The structure of the polyps is, in its general features, Actinian, but there 
is a marked bilateral arrangement of parts. The mouth-disk, with its fringe of twelve 
tentacles, is capable of retraction within the fossa of the corallite. In vertical section of a 
contracted polyp the soft tissues form a funnel-shaped structure similar to that seen in 
Alcyonum under similar conditions. The mouth is elongated in the sagittal axis. The 
stomodeum, which occupies the central portion of the cclenteron, is supported by twelve 
mesenteries, which, however, differ in importance. The extremities of the stomodzum are 
* “Anatomy of the Madreporaria.—Part IT.,” Quart. Journ. Microsc. Science, vol. xxvii. (1886) 
pp- 1-16, pl. i. 
