14 ARTHUR DENDY. 



The Inhalant Canals. 



These commence as widely expanded cavities immediately 

 underlying the pore-areas. These cavities correspond in posi- 

 tion to the subdermal cavities of other sponges, but they 

 merge so gradually into the deeper parts of the inhalant 

 canals, with which they are directly continuous, that it is 

 impossible to distinguish the boundaries between the two. 

 The inhalant canals (intercanals of Haeckel) are by no means 

 regular; they may anastomose and they may branch. The 

 anastomosis takes place — most frequently, at any rate — ^just 

 below the surface, so that the pores of two contiguous areas 

 may lead almost directly into one and the same inhalant 

 canal. The branching takes place chiefly at the far end of 

 the canals, towards the gastral surface. 



At first very wide, the inhalant canals, as they penetrate 

 below the dermal cortex and between the flagellated chambers, 

 rapidly diminish in diameter, and finally come to an end just 

 below the gastral cortex where the flagellated chambers are 

 just commencing (figs. 25, 26, in. c). In figs. 28 and 29, 

 which represent sections taken at right angles to the long 

 axes of the flagellated chambers, the inhalant canals are seen 

 cut transversely between the chambers. In fig. 28, which 

 represents a section taken not very far from the middle of the 

 sponge-wall, the inhalant canals are still wide ; but in fig. 29, 

 which represents a section from near the gastral surface, the 

 inhalant canals have become very much reduced in size. 



The Prosopyles. 



The term '' prosopyle '' is used by Sollas (9) to designate the 

 openings of the inhalant canals into the flagellated chambers, 

 and to distinguish them from the inhalant pores on the surface 

 of the sponge. As it is a decided advantage to employ two 

 separate terms for these two very distinct structures, I shall 

 adopt Sollas's nomenclature. 



The prosopyles in Grantia labyrinthica are numerous 

 small circular apertures, each about 0*018 mm. in diameter, 



