STUDIES ON THE COMPAEATIVE ANATOMY OP SPONGES. 199 



shorter oxeote spicules usually projecting more or less at right 

 angles therefrom. The skeleton of the chamber layer^ on the 

 other hand, consists of irregularly scattered triradiates or 

 quadriradiates. 



In some species, e.g. L.phillipensis and L.austr alien sis, 

 the quadriradiates of the gastral cortex are continued inwards 

 along the larger exhalant canals, which possibly indicates a 

 folding of the wall of the gastral cavity, though I do not think 

 it necessarily does so. 



In some species, e.g. L. phillipensis, we find many of the 

 triradiates of the chamber layer retaining their primitive 

 sagittal character, and with the basal ray pointing towards 

 the dermal surface. This may be a reminiscence of the time 

 when they formed part of an articulate tubar skeleton. Sub- 

 gastral sagittal triradiates may also still be present (figs. 

 16, 17). 



Lelapia. 



In this genus of a single species the canal system is un- 

 known, and the skeleton is peculiar. The skeleton of the 

 gastral cortex is composed of ordinary radiates ; while that 

 of the dermal cortex is composed of triradiates, quadri- 

 radiates, and minute oxea. The skeleton of the chamber layer 

 is composed of large, longitudinally arranged oxea, crossed at 

 right angles by bundles of tuning-fork shaped triradiates whose 

 basal rays point towards the dermal surface. For further 

 particulars I must refer the reader to Mr. Carter's description 

 of the sponge (12), as I have never had an opportunity of exa- 

 mining it myself. 



I should, perhaps, mention that Mr, Carter describes the 

 occurrence of small quadriradiate spicules "on the surface,^' 

 presumably in the dermal cortex. Triradiate spicules are very 

 apt to develop an apical ray, often so small as to be of no con- 

 ceivable use, and apparently indicating a mere "sport,^' if one 

 may use the term. Therefore, unless the feature could be 

 shown to be constant, well established, and characteristic, I 

 should not be inclined to attribute any great value to it. It 



