118 I. IJIMA : HEXACTINELLIDA. I. 



protuberances. Assuming that mass to be free of the trabeculae 

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

 externally and internally in making up the choanosome, there 

 should lead out proxiraad from it numerous, separately opening 

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

 give molding to the excurrent canals of the choanosome. 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 Sycons, forms a part of the general system 

 of incurrent spaces. iVlong the course of the incurrent canals 

 penetrating into the choanosome, the interspace just mentioned 

 is more or less wide ; 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 trabeculse in their relation to tlie above mass of the 

 chamber-layer show in the original primitive condition the 

 following arrangement : The outer trabecular system forms a 

 continuous superficial layer, coveiing 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 hollow^s of the 

 evaginated chamber-layer. In shoit, we may consider the entire 

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

 network of thin trabeculœ 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 alw^ays 



