12 ARTHUR DENDY. 



embrace the chamber which they help to support. This is 

 seen in figs. 28 and 29^ where, owing to the direction of the 

 section at right angles to the long axes of the flagellated 

 chambers, the shafts of the triradiates are cut off", while the 

 paired lateral arms are seen partially surrounding the chambers. 



The Skeleton of the Stalk. 

 This consists essentially of a confused mass of closely inter- 

 woven sagittal triradiates with very long and slender arms. 

 One of these spicules is represented in fig. 19 ; often they are 

 more or less irregular in form. Ou the extreme outside there 

 is a layer of oxeote spicules disposed at right angles to the 

 surface. Most of these spicules are small, and very like those 

 found over the surfaces of the cup, but a large number are 

 modified into giant forms (fig. 12), diff'ering somewhat in shape 

 from those which form the oscular fringe. These giant 

 spicules give to the surface of the stalk a more or less hispid 

 character. They are remarkable from the fact that they 

 project to an unusual extent, so that commonly less than a 

 quarter of the length of the spicule is embedded in the tissues 

 of the sponge. The outer ends of the spicules are consequently 

 generally worn or broken. 



(d) The canal system. 



Grantia labyrinthica appears to agree more closely with 

 respect to the arrangement of the canal system with Haeckel's 

 Sycortis la3vigata (7) than with any other described form. 

 The canal system of all the Sycons is, of course, fundamentally 

 the same, but numerous, by no means insignificant, variations 

 occur, especially with regard to the inhalant pores and canals. 



The canal system of calcareous sponges may be described in 

 precisely the same terms as that of the siliceous and horny 

 sponges, and since it is advisable to preserve uniformity of 

 nomenclature wherever possible, I shall follow Polejaeft''s 

 example (8) in making use of such general terms as '' flagel- 

 lated chamber" and "inhalant canal " in preference to such 

 special terms as "radial tube" and "intercanal" used by 

 Haeckel for the Calcarea. The term " gastral cavity " I pro- 



