542 
SPONGES. 
•■WMl 
silfes* ' 4 
*m h 
i 
W; .■ K % 
W| 
Sfe • 
CS4 
^'i : ' * 
I 
gjf ^ 
sponges; the siliceous needles becoming less numerous and the horny substance 
more abundant, till, in the true horny sponges, such as the toilet-sponges, the 
skeleton consists entirely 
of horny fibres. The 
ocellated Chalina, fre¬ 
quently cast ashore round 
the British coasts, ex¬ 
hibits an intermediate 
condition between the 
siliceous and horny forms. 
By teasing out and ex¬ 
amining a few fibres under 
the microscope, a fine 
core of siliceous spicules 
will be seen in the axis of 
each thread of spongin. 
The illustration on 
p. 528 represents a group 
of sponges growing to¬ 
gether. Near the base of 
the black seaweed on the 
stone there arises the 
much-branched Desmaci- 
dine sponge, so called 
from its buckle - shaped 
spicules; while from the 
left branch of the former 
grows a flat alga encrusted 
by another sponge of the 
same order, and of a dull 
yellow colour; and at the 
top of the colony is the 
violet Spongelia. The 
illustration to the left 
represents another sponge 
of this group ( Axinella ), 
common in the Mediter¬ 
ranean. In life this 
sponge is of a yellowish 
colour, and the oscules present a radiate 
arrangement like the polyps of a branch of 
fan-coral. The illustration on p. 543 illustrates 
a sponge dredged by the Challenger, and known 
as Esperiopsis challengeri, from six hundred 
and thirty fathoms, east of the Celebes. The largest specimens are about 8 inches 
in height. From a solid, strong stem six or seven stalks are given off at gradually 
m 
m 
A SINGLE-llAYED SPONGE, 
Axinella (nat. size). 
SILICEOUS SPICULES OF MONAXONID SPONGES 
(magnified 200-300 diameters). 
