494: A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



These canals vary very much in size. The measure from 0*25-1 

 mm. in diameter. In the digitate and lobate processes they extend 

 mainly in a longitudinal direction. Vexy few and scattered larger 

 inlialent canals extend from these downward into the interior of 

 the sponge. 



They ramify very much, and so, a great many cylindrical canals 

 ai-e produced, which extend mainly in a longitudinal direction. 

 They measure 0-05 mm. in diameter, and are surrounded by 

 ciliated chambers of the ordinary shape and size. The latter open 

 into wider exhalent, likewise longitudinally disposed, and circular 

 canals which measure on an average 0-2 mm. in diameter and coal- 

 esce to form irregularly disposed canals which lead, extending in a 

 tangental direction, towards the extensive lacunes of the exhalent 

 system. 



I have mentioned above that the oscula are usually surrounded 

 by acanulovis zones, and we find that these zones are destitute of a 

 skeleton and are represented in dry skeletons by irregular grooves 

 and depressions. We find these askeletous parts, which are more 

 highly developed in Euspongia canaliculata, and which will be 

 minutely described under that heading, filled with a very lacunose 

 tissue with fewer chambers, and much larger exhalent canals than 

 in the askeletous parts of the sponge. These large exhalent canals 

 join to form a very short oscular tube. Often no oscular tube at 

 all is developed, and the membranes which divide the lacunae reach 

 nearly up to the osculum itself. 



Skeleton. (Plate XXXVI. , fig. 3.) 



The differences of the four varieties are mainly found in 

 difierences of the skeleton. 



The skeleton of all the specimens agree in the following points : — 



The main fibres are cored with foreign bodies, and on an average 

 1 mm., apart. They are not much curved and extend radially 

 from the base of the sponge upward and outward and are mostly 

 branched in a penicillate manner. 



