538 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



They are not very numerous, and there is only one single layer of 

 them. The firm substance between them is about as voluminous 

 as the canal space. 



Towards the centre of the lamella large exhalent lacunose canals 

 are met with, which unite to form an oscular tube, tending 

 upward and terminating with the cii'cular osculum on the lamella 

 margin. 



Between these two canal-systems smaller canals, averaging 

 0'05 mm. in diameter are met with, these have mostly a circular 

 transverse section and extend in a longitudinal direction. Some 

 of them are exhalents, others inhalents. Between them the 

 ciliated chambers, which are spherical and represent about three- 

 quarters of spheres, are met with. They measure 0-037 mm. in 

 diameter. 



Skeleton. (Plate 36, Hg. 2.) 



The skeleton resembles that of Euspongia officinalis pretty 

 closely. The main fibres are slightly branched and disposed longi- 

 tudinally. They are free from foreign l)odies, and on an average 

 0"1 mm. thick. 



The connecting fibres form a very i-egular network. No 

 secundary and tertiary fibres as in Etispongia canaliculata can be 

 distinguished. All the connecting fibres are free from foreign 

 bodies and 0-016 — 0.032 mm. thick. The most connecting fibres 

 measure about 0-025 mm. 



The meshes of the connecting fibre network are on an average 

 Q-l mm. wide. They become smaller in the vicinity of the main 

 fibi-es. 



Here and there we find large sand grains measuring 0-2 — 

 0*4 mm. enclosed and embodied in the skeleton. These 

 resemble the sand-grains forming an essential part of the skeleton 

 of Aulena villosa, very closely. They are found occasionally in the 

 network of the connecting fibres, but generally in the main fibres. 



In the outer skin occasionally similar sand grains are met with, 

 and there is no doubt that the sponge grows around these and so 

 they become imbedded in it. Where the large sand grain has been 



