STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 169 



of adjacent chambers does not commence until a short distance 

 within "this pore-bearing membrane, so that the dermal pores 

 lead at first into a continuous subdermal space, from which 

 the true "inter-canals" penetrate between the chambers. 



In another Australian species, to which I have given the 

 name Sycon boomerang (4), we meet with yet further com- 

 plication. The principal features in the anatomy of this 

 species are shown in figs. 7 and 8. The radial chambers are 

 very long, thin-walled, and very much branched, especially 

 towards their distal ends.^ The irregularity in the branching 

 causes the tufts of oxea at the distal ends of the chambers to 

 form an irregular series of prominences on the surface of the 

 sponge (fig. 8). Owing to the branching of the chambers the 

 inhalant canal system also becomes very irregular. The wall 

 of the gastral cavity is rather thick, and the length of the 

 exhalant canals appears to be further increased by an irregular 

 and not very extensive folding of the same (fig. 7). As in S. 

 gelatinosura, a thin pore-bearing membrane extends be- 

 tween the ends of the radial chambers, but in S. boomerang 

 a few spicules are found in tliis membrane (fig. 8). 



In Sycon giganteum (4), a very large species from the 

 Gulf of St. Vincent, which closely resembles S. gelatinosum 

 in structure, the radial chambers are narrow and greatly 

 elongated ; they branch repeatedly, and the branches run 

 parallel with one another to the dermal surface. They com- 

 municate with the gastral cavity through rather long exhalant 

 canals, which commence at some distance beneath the gastral 

 cortex. These canals appear to have been formed by modifi- 

 cation of the proximal portions of the radial chambers, from 

 which they are separated as usual by diaphragms. They may 

 unite together before opening on the gastral surface. The 

 inhalant canals are irregular and very narrow, opening on the 

 dermal surface through narrow, irregular chinks between the 

 tufts of oxeote spicules which cram the distal ends of the 

 chambers. I have not been able to detect any pore-bearing 



^ It appears from Schulze's researches that branching of the chambers 

 may take place even iu such a simple form as S. raphanus (7). 



