O-i Proceedings of iJie Royal Society of Victoria. 



Numerous flagellated chambers open out of one and the 

 same ultimate inhalant lacuna. The chambers themselves 

 are more or less spherical sacs, about 004 mm. in diameter, 

 with two wide aperture?! of about ec^ual size placed at 

 opposite }>oles, whei'cby they communicate on the one hand 

 with an ultimate iidialant lacuna, and on the other with an 

 ultimate exhalant lacuna. Several chambers may lead into 

 one and the same ultimate exhalant lacuna. 



Both the inhalant and exhalant apertures of the flagellated 

 chambers are usually drawn out into short and relatively 

 wide cameral canalieuli, much as in Enspougia officiitalls, as 

 figured ])y Schulze. 



The exhalant canal system is partly lacunar and partly 

 composed of very definite tubular canals (the oscular tubes) 

 with proper walls of their own, separable from the remainder 

 of the choanosome. The ultimate exhalant lacunse, into 

 which thc^ flagellnted chambers open, collect together and 

 finally discharge their contents into Ijranches of the oscular 

 tubes. Each oscular tube is a })erfectly definite, wide, 

 cylindrical cannl, with distinct walls, and leads vertically 

 upwards to a wide circular osculum situated on the upper 

 margin of the sponge. 



In connection with the exhalant canal system, I must 

 also mention certain spherical cavities lying in the 

 neighboiu'hood of the oscular tubes, and containing each a 

 single large embryo. These cavities appear now to be 

 entirely closed and cut off" from the remainder of the canal 

 system of the sponge, but it is possible that they are really 

 poi-tions of the exhalant canal system, specially modified to 

 serve as receptacles in which the embryos aie lodged during 

 a large ]>ortion of their development. 



(d) Histology of the Soft Tissues. 



A. The Ectosome. — The ectosome forms an external layer of 

 varying thickness all over the surface of the sponge. Owing 

 to the presence in it of a large amount of sand, especially 

 abundant on the raised ridges, it is very hard and tough, and 

 forms an excellent })rotection against the attacks of jnirasitic 

 crustaceans, worms, &c., to wdiicli sjionges are very subject. 



The outermost layer of the ectosome is formed by an 

 extremely thin and delicate epidermis, most readil}^ visible 

 in the pore-areas, where the sand grains are absent. The 

 nuclei of the epidermic cells may be easily distinguished in 

 the transparent ]iore-bearing membi'ane ; they are round or 

 oval in shape, and about 0-0()4-8 mm. in diameter. 



