306 



PLATE LXXXVII. 



length of those composing the fasciculi. The whole of 

 the skeleton spieula agree in the mode of the attenua- 

 tion of their forms, it commences very near tlic Ijasc 

 and continues to the slender and acute distal termina- 

 tion. Their basal terminations vary consideraljly in 

 shape ; some are more or loss inclined to be spinulated ; 

 in others they are slightly attenuated, while the greater 

 portion are purely acuate. In some the spination of 

 the basal extremity is so incipient as scarcely to be 

 visible, while in others it is more distinctly produced ; 

 but it never seems to extend much beyond the base of 

 the spiculum. 



The cylindrical, entirely spined, tension spieula of 

 the basal membrane are very numerous ; they vary 

 somewhat in their forms, many of them being inequi- 

 cylindrical to such an extent as to closely approach the 

 acuate form ; but the normal form is cylindrical. 



Their mode of disposition is very irregular ; occa- 

 sionally tliey are fasciculated, three or four together ; 

 but the greater portion of them are irregularly dispersed 

 over the surface of the membrane. 



The retentive spieula are the same as those of the 

 dermal membrane, and as in that organ they are rather 

 few in number. 



The internal defensive spieula are numerous ; they 

 are projected from the basal membrane at about right 

 angles to its plane, and they pass through the substance 

 of the sponge to very near its external surface. They 

 all agree in form, but vary to a considerable extent in 

 length. 



