SYCANDRA. 103 
CHAPTER XII. 
IVPE OF PORIFERA. 
SYCANDRA. 
PHYLUM PORIFERA. 
Cass CALCAREA. 
Sycandra compressa isa small marine 
sponge of a dull yellow tint, found fixed 
to rocks or weeds between tide marks. 
It is in shape like a flat- 
tened flask and varying in 
length up to 14 inch, It 
is like all sponges axially symmetrical 
(though the symmetry is often obscured), 
hence we can distinguish merely a main 
axis, a base, and an apex. The base is 
fixed to a foreign body and the apex 
has a large opening, the oscudum, which Fixed to sea-weed, with bud , 
leads into the interior of the sponge. parila 
If the living Sycandra be watched carefully in a vessel of 
water, it will easily be seen that currents of water are, with- 
out intermission, pouring out of the osculum. Further 
examination of the surface of the sponge would reveal an 
immense number of extremely minute openings all over the 
surface, into which the water perpetually flows. These are 
termed the pores. ’ 
If a hand-section of the sponge be made it is seen 
to be hollow, and the wall appears of even thickness all 
round the central cavity. This cavity is called the para- 
gastric cavity, opening through the osculum to the exterior. 
The walls of the sponge are of a somewhat firm leathery 
consistency and when boiled in potash the 
animal matter is destroyed, leaving a residue 
of numerous small spicules, transparent and 
tri-radiate in shape. These hard spicules dissolve immedi- 
ately, with effervescence, on the. application of any dilute 
Fig. 37.—SYCANDRA 
COMPRESSA. 
Osculum. 
Form and 
Habits. 
Internal 
Structure. 
