302 W. WOODLAND. 
mesogloea does not form such a solid mass enabling the 
spicules to be distantly situated from any limiting layer, “ the 
majority of the spicules are elongated needles and spindles, 
and there is an entire absence of the small dumb-bell-shaped 
forms, very few Ks. and crosses [i.e. both resembling figs. 
13 and 14], and there are several club-shaped forms [essen- 
tially monaxon spicules with fairly conspicuous processes and 
thickened towards one end, which occur in the most deeply 
situated portions of the mesogloea], which I have never seen 
in any preparation of A. digitatum.” ‘It is true that 
many of the elongated and spindle-shaped spicules of A. 
glomeratum are almost exactly the same shape as the 
spicules of the tentacles and disc of the polyps of A. digita- 
tum, but the clubs are peculiar to it, the dumb-bell [not my 
developmental dumb-bell] absent, and the Ks. and crosses 
very rare.” Further evidence in support of this general con- 
clusion that the nearer a spicule is situated to a limiting layer 
the more regular will be its form, is supphed by von Koch in 
his account of the spicules in Clavularia prolifera already 
referred to, where he gives figures showing that spicules situ- 
ated near the surface are quite regular in form (stick-like), 
but that spicules situated in deeper layers of the mesoglcea 
become irregularly branched, but never massive and tree- 
like, as in A. digitatum, since the colony of Cl. prolifera 
is very racemose in form. Other Alcyonaria supply like evi- 
dence, as may be seen, e. g., by glancing through the plates 
in the ‘Challenger Report’ on the Alcyonaria. It is also 
worthy of note that when as in Calcareous Sponges and certain 
Holothuria the body-wall is very thin, and the contained 
spicules therefore necessarily in close apposition to both 
external and internal epithelia, these are in general remark- 
able for their definiteness of form, 
