174 ARTHUR DENDY. 



tube surrounding the central gastral cavity is about 1 mm. 

 thick, and is divided into two sharply defined concentric layers 

 of about equal thickness. The outer of these layers forms a 

 firm cortex, with a very strongly developed skeleton. The 

 inner layer is soft and spongy, consisting almost entirely of 

 the thin-walled radial chambers. 



Fig. 11 represents a portion of a transverse section of the 

 sponge. It will be seen from this that the radial chambers 

 are arranged side by side with great regularity. Each is a 

 straight, wide, unbranched (or very slightly branched), thin- 

 walled tube, extending completely through the chamber layer. 

 In cross-section the chambers vary from nearly square to 

 nearly circular. Each opens directly and separately into the 

 gastral cavity, the gastral cortex being so thin that no special 

 exhalant canals are required. Each is provided at its proximal 

 end with a membranous diaphragm, which, in spirit specimens, 

 almost closes the exhalant opening. There is, of necessity, a 

 well-developed cortical inhalant canal system. The inhalant 

 pores, scattered over the dermal surface, lead into sharply 

 defined cortical canals, which unite into larger trunks, which 

 conduct the water to the ordinary '^'intercauals^' between the 

 radial chambers. Hence it appears that, as regards the canal 

 system, the points to be specially noticed in Grantiopsis are 

 the strong development of the cortical canal system and the 

 great elongation of the gastral cavity. 



Ute (figs. 12—14). 

 The canal system of a typical Ute agrees essentially with 

 that of a typical Gran ti a. In Ute syconoides (4) the canal 

 system is unusually regular, and the radial chambers have a 

 remarkably definite and constant form. The anatomy of this 

 species, which in general form closely resembles the European 

 U. glabra, is represented in figs. 12 — 14. The radial 

 chambers are straight, and circular in transverse section for 

 the greater part of their length (fig. 13). Towards their 

 distal extremities, however, they widen out in a direction at 

 right angles to the long axis of the gastral cavity of the 



