PLATE LXXXII. 271 



In a small slice from the surface of the sponge, 

 mounted in Canada balsam, the pores were distinctly 

 and beautifully exhibited in the spaces between the 

 heads of the groups of the ternate connecting spicula. 

 They were in an open condition and were comparatively 

 of large size. The dermal surface is remarkably dense 

 and strong in consequence of the abundance of the 

 closely packed and numerous corymbose fasciculi of the 

 connecting spicula, the terminal heads of which serve 

 to a great extent as external defences. Amidst these 

 fasciculi large skeleton spicula are rather sparingly 

 projected for about half their length, forming the 

 primary external defensive system, and amidst these 

 the long and slender secondary defensive spicula are 

 projected ; they are not very abundant, but much more 

 so than those of the primary system. The dermal 

 membrane is profusely furnished with two forms of 

 stellate, retentive spicula. The first one is attenuato- 

 stellate with their radii few in number, long and very 

 acutely terminated, and they are four or five times the 

 diameter of the smaller series, which are very minute 

 cylindro-stellate forms with numerous radii. They are 

 indiscriminately mixed and dispersed, the smaller ones 

 being very much the most numerous. 



The connecting spicula are remarkable by their 

 great number as well as by their form. They are 

 large and stout with very short radii, which in the 

 adult state are bent suddenly downwards near their 

 distal terminations. They are disposed at the surface 

 of the sponge in large closely packed fasciculi ; their 

 bases are closely pressed together, their shafts radiat- 

 ilig to such an extent as to bring all their distal ter- 

 minations into the corymbose form. 



The interstitial membranes are furnished abundantly 

 with the same forms of retentive spicula as those of the 

 dermal membrane. The doliolate spicula are large and 

 few in number. 



The habit of collecting such a profusion of small 

 pebbles and other extraneous matters on its surface to 



