STUDIES ON THE COMPARATIVE ANATOMY OP SPONGES. 183 



in the neighbourhood of Port Phillip. The sponge is colonial, 

 and consists of short, thick, subcylindrical or truucatedly conical 

 individuals, united together basally in larger or smaller agglo- 

 merations. Each individual has a single well-defined wide 

 gastral cavity, with a single terminal osculum, protected by a 

 remarkably distinct membranous diaphragm situated a short 

 distance within its margin. The wall of the sponge surrounding 

 the gastral cavity is thick, and there is a dense thick cortex on 

 both gastral and dermal surfaces. Between the dermal and the 

 gastral cortex lie the flagellated chambers, thickly but irregu- 

 larly scattered. These chambers vary to a remarkable extent 

 both in shape and size, from approximately spherical ones of 

 about 0*072 mm. in diameter, to elongatedly sac-shaped ones 

 of as much as 0'37 by 0*13 mm. It is right to state that these 

 measurements were taken from different specimens, but the 

 species is so well characterised that it would be difficult to 

 make a mistake in identification, and we also find considerable 

 variation in the chambers, even in the same section. Most 

 remarkable, however, is the inhalant cortical canal system, a 

 portion of which, from an osmic acid preparation, is represented 

 in fig. 23. The inhalant pores, thickly scattered over the 

 surface of the sponge, lead each into a separate narrow canal 

 lined by a flattened epithelium. These canals unite together 

 into larger and larger canals as they penetrate the dermal 

 cortex, and also form frequent anastomoses by cross-branches. 

 This canal system conducts the water to the chamber-bearing 

 layer of the sponge wall and distributes it to the chambers; 

 from these it is collected again by the exhalant canals, which, 

 uniting into tolerably large trunks, penetrate the gastral cortex 

 and open into the central gastral cavity. I have never seen 

 the inhalant cortical canal system so well illustrated as in this 

 sponge, doubtless because I took the precaution to treat a 

 piece of a living specimen with osmic acid. It finds a close 

 parallel in the corresponding cortical canal system of the 

 Syconoid Grantiopsis cylindrica, and may probably be 

 taken as representing the typical condition for Heterocoela 

 having a very strongly developed dermal cortex. 



