312 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



The first reason put forward as possible for tlieir formation in 

 Halme cannot hold good here, as there is no cortical lamella to 

 the sponge at all. Also in this genus the resemblance to certain 

 Auloplegma forms of calcareous sponges is very striking. 



The whole structure may be a somewhat changed remnant of an 

 organ previously possessed by sponges, and lost in all, except the 

 Auleninse. In this case we would have to consider Aulena as still 

 more conservative than Halme. 



I have however, no knowledge of the embryological development 

 of either genus, so that I must leave it to the thinking reader to 

 draw his own conclusions from the facts described. 



Canal System. 



The canal system of our sponge is more complicated than that 

 of Halme, but still more simple than in most other sponges. 



The inhalent pores are scattered all over the surface and on an 

 average 0'2 mm., apart. They are circular or oval and apparently 

 very liable to changes in shape and size, as their dimensions differ 

 in ditJ'erent specimens and also in different parts of the same 

 specimen. No regularity in these differences could be traced and 

 I therefore believe that they are of the same size throughout the 

 sponge and that they can be contracted and dilated at the option 

 of the sponge. 



I estimate the average diameter at 0-04 mm. Outside they are 

 covered by a very fine and tender sieve membrane, with numerous, 

 about twenty, circular pores. I have repeatedly found this sieve 

 membrane absent in spirit specimens, which were preserved by 

 myself and ought to have shown it. Possibly this is due to the 

 extreme tenderness of it. The rapid contracting effect of the 

 alcohol may have x^uptured them. 



The inhalent pore is the opening of a short, circular and cylin- 

 drical canal, about 0-04 mm., long and as wide as the pore itself, 

 which pervades the skin of the sponge and leads into the subdermal 

 cavity. 



The latter is not so highly developed as in Halme and consists 

 of a system of wide anastomosing canals extending tangentally and 



