PORIFEEA [sponges]. 



35 



(Ti-oups of whip chambers lead each by a short passage into a common High Cases 

 channel, which joins with other canaliculi to form canals, finally Table clte l 

 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. 



OSCllif I 



A 



Toilet 

 b, 



c. 



Sponge. A. Diagram of Canal System, b. 

 canals ; c, whip-chambers ; d, skeleton fibres 



Whip-chambers. Highly magnified. (After F. E. Schiilze.) 



Section showing a, pores ; 

 d', main fibre ; e, embryo. 



thin ^alls. The Common Bath Sponge is, in fact, composed of 

 contorted lamellae separated by labyi-inthine 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 l)ath sponge and fine toilet sponge growing on it. 



The Spongki zimocca, or Hard Sponge, which forms a third species 



D 2 



