Art. VIIT. — Preliminary Notes on the Structure and 

 Development of a Horny Sponf/e {Stelospongus fiahelli- 



formis). 



By Arthur Dendy, M. Sc, F.L.S. 



Demonstrator and Assistant Lecturer in Biology in the University of 

 Melbourne. 



[Read July 12, 1888/ 



I. — Anatomy and Histology. 



(«) External Characters. — This sponge, which was 

 discovered by Mr. J. Bracebridge Wilson, M.A., near Port 

 Phillip Heads, Victoria, and briefly described b}- Mr. H. J. 

 Carterin the Annals and Magazine of Natural History, consists 

 of a stout cylindrical stalk terminating below in a basal 

 expansion for attachment to the substratum and above in a 

 broad, compressed, but thick frond. Along the upper 

 margin of the frond is a single row of large oscula. 

 The character of the surface of the frond is subject to 

 considerable variations. On both sides it usually exhibits a 

 number of prominent, branching and anastomosing ridges, 

 enclosing a number of concave depressions. The entire 

 surface of the sponge is more or less thickl}' encrusted with 

 particles of sand ; these are, however, more abundant over 

 the ridges than in the depressions, and the latter are 

 characterised by a minutely reticulate appearance, due to the 

 presence of the inhalant pore-areas. The pores are enormously 

 abundant all over the depressed portions of the surface, but 

 are absent on the ridges. 



(b) Skeleton. — The skeleton is composed of a rather 

 irregular reticulation of cylindrical horny fibres, branching 

 and anastomosing freely. The filires are rather slender and 

 the meshes between them are wide. It is easy to distinguish 

 primary and secondary fibres. The primaries are long and 

 rather stouter than the secondaries, about 0'096 mm. in 

 diameter. They radiate towards the surflice of the sponge, 

 and end in the sandy incrustation. They are easily 



