10 AETHUE DENDY. 



sagittal triradiates represented in figs. 13 and 14 occur 

 also in the gastral cortex ; and here, too, we meet with 

 the quadriradiate spicules. The latter surround the short 

 exhalant canals of the flagellated chambers, being arranged as 

 shown in figs. 21 and 24, with the additional fourth ray pro- 

 jecting towards or into the lumen of the canal. Occasionally 

 an unusually small exhalant canal is met with, cut transversely, 

 in tangential sections of the cup-wall, a little below the level 

 of the ordinary exhalant canals. Such small canals (fig. 21) 

 are surrounded by quadriradiate spicules of the slightly different 

 form already described. 



On the extreme outside of the gastral cortex (i. e. the extreme 

 inside of the cup-wall) there occur abundant oxeote spicules 

 like those of the dermal skeleton, and arranged, in close-set 

 tufts, perpendicularly to the surface with their broad ends 

 outwards (fig. 22). Mr. Carter (3) states that the linear 

 (oxeote) spicules on the " vent-side " of the cup-wall are twice 

 the length of those on the '' pore-side." This does not hold 

 good as a general rule, for in the specimen before me the 

 reverse is the case (fig. 22). 



The Skeleton of the Peristome. 

 This consists of a fringe of the giant oxeote spicules already 

 described (figs. 7 — 9), arranged with their broad ends pro- 

 jecting freely around the margin of the osculum, and their 

 narrow ends embedded amongst a mass of approximately equi- 

 radiate triradiates, into which the dermal and gastral skeletons 

 merge. The oscular fringe (fig. 25, o. sp.) thus formed is so 

 very slightly developed in proportion to the size of the whole 

 sponge that it is scarcely noticeable with the naked eye. 



The Tubar Skeleton. 



According to the manner in which the spicules are arranged 



around the flagellated chambers (radial tubes) Haeckel (7) 



distinguishes two types of tubar skeleton, (1) articulate (geglie- 



dertes) and (2) inarticulate (ungegliedertes). The articulate 



