118 I. IJIMA : HEXACTINELLIDA. I. 



protuberances. Assuming that mass to be free of the trabecuhc 

 and the spicules, with which it in reality is connected both 

 externally and internally in making up the cboanosome, there 

 should lead out proximad from it numerous, separately opening 

 tubular passages, not unlike the radial tubes of Sycons and wliich 

 give molding to the excurrent canals of the cboanosome. Ex- 

 ternally, between and around the contiguous, irregularly shaped 

 protuberances, there should exist, this time not tubular passages, 

 but an exceedingly intricate and continuous interspace, which, 

 like the intercanals of 8ycons, forms a part of the general system 

 of incurrent spaces. Along the course of the incurrcnt canals 

 penetrating into the cboanosome, the interspace just mentioned 

 is more or less vvide ; at most other places, especially in the 

 deeper region, it is quite narrow and often exceedingly com- 

 pressed in that the external surfaces of chambers, belonging either 

 to the same or different protuberances, come nearly or even 

 quite into contact with one another. 



The trabeculae in their relation to the above mass of the 

 chamber-layer show in the original primitive condition the 

 following arrangement : The outer trabecular system forms a 

 coutinuous superficial layer, covering over the outer ends of the 

 chamber-layer evaginations and thence extends alike into all 

 parts of the afferent interspace between the latter ; similarly, the 

 inner trabecular system continuously covers the inner surface of 

 the sponge-wall and also pervades all the efferent hollows of the 

 eva2;inated chamber-laver. In short, we mav consider the entire 

 thickness of the sponge-wall as consisting of a nearly uniform 

 network of thin trabeculse which keep the folded chamber-layer 

 suspended midway between the two surfaces of the wall. Such 

 a comparatively simple arrangement of the soft parts is always 



