STUDIES ON THE COMPARATIVE ANATOMY OP SPONGES. 185 



Leucilla (figs. 21, 23). 



This genus includes species which never possess a truly 

 radiate Syconoid type of canal system, but either a thoroughly 

 typical Leuconoid arrangement with small, more or less 

 rounded chambers, as in Leucilla australiensis (fig. 22), 

 L. saccharata, and L. prolifera (4), or an arrangement like 

 that of Leucilla uter (fig. 21), which indicates by the 

 elongated form of the chambers and their radial arrangement 

 around the exhalant canals a Sylleiboid condition, intermediate 

 between the Syconoid and Leuconoid types. 



The genus Leucilla, in short, occupies a position in the 

 family Amphoriscidse exactly analogous to that occupied by 

 Leucandra amongst the Grantidae, and we fiud in both 

 genera the same variations in canal system. Thus the canal 

 system of Leucilla uter^ appears to be almost exactly paral- 

 leled by that of Leucandra aspera (14), while that of 

 Leucilla australiensis and the other species with small, 

 rounded, and irregularly arranged chambers, is paralleled by 

 the similar arrangement found in numerous species of Leu- 

 candra, as will be evident on comparing figures 16 and 22. 



Most remarkable is the canal system of Polejaeff's Leucetta 

 vera (8), which appears to belong to the genus Leucilla as 

 now constituted. In this species, according to Polejaeff (8), 

 the chambers of the inner half of the sponge wall are rounded 

 and irregularly scattered, while those of the outer half are elon- 

 gated and radially arranged, and it thus afi'ords a noteworthy 

 commentary on the value of the canal system for purposes of 

 classification. 



A similar variation in the form of the chambers, only on a 

 much smaller scale, is to be found in Leucilla australiensis 

 (fig. 22). 



Another interesting variation in the canal system is afforded 

 by Leucilla cucumis (HaeckeFs Leucandra cucumis, 5). 



^ Eor further informatiou as to this species vide Polejaeff (8). My draw- 

 ing is made from my own preparations of a portion of the type specimen from 

 the British Museum. 



