287 
to our Knowledge of the Spongida. 
between the aculeations, the u patches ” overlying a larger 
cavity beneath, into which many excretory canals may open ; 
or opening singly into the bottom of an excavation. Internal 
structure composed of dense, soft, spongy or areolar sarcode 
of a yellowish-white colour, charged with spicules, and pro¬ 
bably bearing the spongozoa (fig. 4, a a), traversed by the 
fibrous skeleton of the sponge (fig. 4, b) and branches of the 
excretoiy canal-system (fig. 4, e), altogether defined out¬ 
wardly by a tough transparent cortex (fig. 4, cc). Areolar 
sarcode filling up the interstices of the fibroskeleton, whose 
larger branches, being composed of chondroid substance charged 
exclusively with the linear spicules (fig. 2) arranged longi¬ 
tudinally, contrast strongly from their transparency with the 
opaque yellowish-white colour of the areolar sarcode, which 
they permeate in all directions, finally terminating in the 
aculeations of the surface (fig. 4 ,dd), where they are covered 
by the cortex thinning out towards their extremities. The 
dark grey cortical layer, which, on its part, also contrasts 
strongly in translucency and homogeneous appearance with 
the yellowish-white areolar sarcode which it limits towards 
the surface, is l-24th inch thick, composed of wavy parallel 
fibres about l-6000th inch in diameter (fig. 7, a ), arranged 
horizontally, and traversed by a minute white tubular (?) reticu¬ 
lation (fig. 7, b) y which appears to pass inwardly into vertical 
lines (fig. 7,c), altogether indicative of pore-tubulation open¬ 
ing into the subdermal cavities; wavy parallel fibres, when 
teased out, often presenting an attenuated extremity (fig. 8), 
and found to be composed of extremely fine fibrillse (fig. 8, a ). 
Excretory canals furnished with transverse circular folds like 
the valvulce conniventes of the small intestine, often uniting 
into a rwgra’-reticulation (fig. 5,cc); composed of three coats, 
viz. an inner, a middle, and an outer coat (viewing the surface 
of the canal as the outside); the inner coat consisting of wavy, 
parallel, translucent fibres, like those of the cortex, arranged 
longitudinally and in contact with the areolar sarcode (fig. 6, 
a a a a) ; the middle coat consisting of the same kind of fibres 
arranged transversely or circularly upon the last, and confined 
to the folds of the rugae (fig. 6, b b b) ; and the outer coat of a 
mucous layer of cells and granular material (fig. 9), the cells 
in form frequently resembling those of the spongozoa, but 
now without the presence of the cilium (fig. 9, a). The longi¬ 
tudinal appear to be a little larger than the transverse fibres 
(that is, about as l-6000th to l-9000th of an incli in diameter), 
both being compounded of extremely fine fibrillae like those 
of the cortex (fig. 8, a), of whose ultimate form I am ignorant; 
while the outer or epithelial layer, being apparently composed 
