346 
ARTHUR DENDY. 
Embedded in this granular matrix may be observed, scattered 
here and there, small nucleated cells of irregularly rounded 
outline (figs. 6, 10, m. c.), doubtless the amoeboid cells of 
authors. This ground tissue appears to agree thoroughly 
with that which Schulze has described (15) as existing in 
Euspongia. 
(5) The Spongoblasts and other Mesodermal Cells 
surrounding the Skeleton Fibres. 
In most parts the skeleton fibres are surrounded by a sheath 
of ordinary stellate and slightly fibi’ous connective tissue. In 
some places, however, doubtless those in which growth of the 
fibre is going on and active secretion is taking place, the stel- 
late mesodermal cells are specially modified as spongoblasts 
or glandular cells whose function it is to secrete the spongin of 
which the horny fibre is composed. In Stelospongus 
flabelliformis these spongoblasts have the form indicated 
in fig. 11, and they form a layer one cell thick around the 
fibre. Each spongoblast is a somewhat club-shaped, slender, 
elongated, granular mesodermal cell, about 0 048 mm. in 
length. One end is drawn out into a long, gradually tapering 
neck, and the other broader end is usually rounded off (but 
sometimes stellate), and contains a spherical nucleus. The 
whole cell is frequently more or less bent or contorted; its long 
axis, however, always lies approximately at right angles to the 
surface of the fibre against which its narrow end abuts. There 
is commonly, if not always, a layer of ordinary stellate meso- 
derm outside the layer of spongoblasts, and it is easy to see 
that the spongoblasts themselves are simply slight local modi- 
fications of the ordinary stellate type of cell, their origin 
being still sometimes plainly indicated by the stellate form of 
the broad end (fig. 11). 
The spongoblasts thus described are practically identical 
with those observed and figured by Schulze in Euspongia 
(15), with the exception that they are very much more elon- 
gated. 
