508 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



evidently a defensive arrangement against foreign intruders which 

 might attempt to get into the body of the sponge from the wide 

 exhalent lacunose or from the oscular tube. 



I.— EUSPONGIA CANALICULATA DURA (Plate 36, fig. 1.) 



The main fibres are slightly and gracefully curved, on an 

 average 1*3 mm. apart they taper towards the distal end which 

 supports the dermal armour of sand. They measure O'l mm. 

 in thickness and have a smooth surface. They are entirely filled 

 with foreign bodies, which are small sand grains measuring for 

 the most part 0-025 mm. with a few short fragments of foreign 

 spicules. 



The connecting fibres are differentiated into primary tangental 

 and secondary radial ones very much more clearly than in the 

 other varieties. The former are on an average 0"3 mm. apart. 

 The primary connecting fibres are either straight or gracefully 

 curved, appearing like ropes supported by the upright main 

 fibres and slightly depressed in the centre. They do not 

 show the slightest trace of curvatures or angles at the joining 

 points. Rarely they devide into two roots in the vicinity of the 

 main fibres. Generally they are perfectly simple thi'oughout, and 

 do not ramify at all. At the base they extend in a trumpet- 

 shaped manner to join the main fibre. They measure 0-03 mm. 

 in thickness on an average. The thickness, however, seems to be 

 in correlation with the length, in as much as the longer fibres are 

 always thicker than the shorter ones. 



The secondary connecting fibres are not regular but still more 

 so than in the other varieties. Many of these fibres are quite 

 simple, and extend in a more or less radial direction, con- 

 necting the pi'imary fibres with each other. They generally do 

 not stand vertical on the primaries, but are more or less oblique- 

 Many appear ramified and altogether they form an irregular net- 

 work of fibres of varying thickness which connects the primaries. 



