35 
PORIFERA [SPONGES]. 
Groups of whip chambers lead each by a short passage into a common High Cases 
channel, which joins with other canaliculi to form canals, finally ^’able Case 1. 
opening by the oscules. The whip chambers form a sort of 
cordon between the extreme rootlets of the in-current and out- 
current canals. 
The horny skeleton, which is imbedded in and which supports 
the tissues of the body, forms a network composed of radiating 
main fibres connected by a dense mesh work of finer secondary 
fibres. 
The Common Bath Sponge, Hippospongia equina , has a massive 
cake-shaped body covered with black or dark skin. The body is 
permeated by wide channels and cavities separated from each other by 
Fig. 18. 
Toilet Sponge, a. Diagram of Canal System, b. Section showing a, pores ; 
b, canals ; c, whip-chambers ; d, skeleton fibres ; d', main fibre ; e , embryo. 
c. Whip-chambers. Highly magnified. (After F. E. Schulze.) 
thin walls. The Common Bath Sponge is, in fact, composed of 
contorted lamellae separated by labyrinthine spaces (Fig. 19) ; the 
large holes on the surface are not oscules, but “ pseudoscules,” the 
true oscules and groups of pores being scattered indiscriminately over 
the surface of the lamellae or walls of the spaces. Currents always 
come out of a true oscule, but they may enter or leave by the holes 
on the surface of the Common Bath Sponge. See specimens in fluid 
in Case I. 
On the floor of Case I. is a broken pitcher with the skeletons of 
a bath spouge and fine toilet sponge growing on it. 
The Spongia zimocca, or Hard Sponge, which forms a third species 
D 2 
