510 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



III. EUSPONGIA CANALICULATA MOLLISSIMA. 



The main fibres of this variety are very diflerent from those of 

 the other varieties. They are on an average 0'9 mm. apart and 

 14 mm. thick. The surface is roughened by a few small knobs. 

 These fibres are never straight or gracefully curved, but appear 

 irregularly bent and twisted a peculiarity which characterises the 

 variety. They contain foreign bodies in great abundance. These 

 are very small sand-grains, measuring only 0-0 14 mm. 



The diflferentiation between primary and secundary connecting 

 Hbres is still less clearly expressed, than in the foregoing variety, 

 although, also in this one, the two can be distinguished at least in 

 certain parts of the skeleton. The primaries are formed of straight 

 portions which join at angles, not so near 180° as in the 

 foregoing variety. Occasionally the portions between the joining 

 points are slightly curved. These fibres ai'e 0'4 mm. apart and 

 on an average 0-032 mm. thick. Their thickness is, however, subject 

 to unusual variations and not proportionate to the length of the 

 fibres as in the other varieties. The secundaries form a very 

 irregular network, and there are no simple unbranched ones at all. 

 The meshes average a diameter of 0-2 mm. The fibres vary very 

 much in thickness from 0008 to 0-03 mm. Some of them are as 

 thick as the primaries. 



It will appear from this that there is a gradation in the develop- 

 ment of the " triplicis " mode of ramification represented by these 

 varieties. That the specimens, which are considered by me as 

 varieties of this species really are very nearly related, can hardly be 

 doubted when it is considered that their anatomy and even shape 

 is so very similar. This shows then that the mode of ramifica- 

 tion of the connecting fibres is not a thing of much systematic 

 value, as has been asserted by Bowerbank and others, and that 

 here again, as in so many other cases the idea of constancy in a 

 certain organ has been broken down by more extensive researches. 



The varieties Euspongia canaliculata mollissi7na and elastica 

 connect the vai-iety dura closely with Euspongia irregularis. A 



