STUDIES ON THE COMPARATIVE ANATOMY OP SPONGES. 173 



the inhalant canal system through distinct, though not very 

 regular, cortical canals. 



I have already, in an earlier paper (9), given a detailed 

 account of the anatomy of the somewhat aberrant and very 

 remarkable Grantia labyrinthica. In its essential features 

 the canal system agrees with that of G. extusarticulata, 

 and there are only two points to which I need refer again in 

 this connection. The first concerns the inhalant pores, which, 

 in this species, tend to be collected together in groups or pore 

 areas, where the cortex forms only a thin dermal membrane, 

 and overlies wide lacunar spaces perhaps comparable to the 

 subdermal cavities of some higher sponges, though not at all 

 sharply separated from the deeper parts of the inhalant canal 

 system. The second concerns the central gastral cavity and 

 osculum, which, though in most calcareous sponges so uniform 

 in structure as to require no special notice, are here enormously 

 enlarged, so that the entire sponge takes the form of a funnel 

 whose thin wall is thrown into deep folds, and the margin of 

 the osculum is no longer evenly curved, but extremely sinuous. 

 Since my memoir on the species was written Mr. Bracebridge 

 Wilson has dredged some very large specimens, one of which 

 measures no less than five inches across the top, so that the 

 actual circumference of the osculum is something enormous. 



Grantia labyrinthica also illustrates very clearly the 

 branching of the radial chambers, which is of very general 

 occurrence in Syconoid sponges higher than the Sycetta 

 type. 



Grantiopsis (fig. 11). 



The only species of this sub-genus, Grantiopsis cylin- 

 drica(4), though evidently derived from the ordinary Grantia 

 type by no very great amount of modification, is in many ways 

 a very remarkable sponge. The entire sponge forms long 

 cylindrical tubes, which may branch and which are provided 

 with single terminal oscula. The largest tube which I have 

 seen is unbranched and slightly crooked, 57 mm. long, and 

 with a nearly uniform diameter of 5 mm. The wall of the 



