58 BRITISH SPOXGIAD.E. 



the contrary, they were directed inward at various 

 angles towards the dermal membrane, or were pros- 

 trate amidst the skeleton fasciculi. This especial 

 application by the sponge of organs of defence against 

 an unusual danger is a very remarkable fact, but it is 

 not a solitary case, as I have met with several other 

 similar instances of provident defences during the 

 course of my investigations of the nature of sponge 

 structures. Independent of those portions of sponge 

 built over the Lepralia cells, there are parts of the 

 sponge deposited upon the smooth surface of the shell 

 that are considerably thicker and more elevated, in the 

 form of minute hummocks, above the surrounding por- 

 tions of the sponge, and such elevations are more or 

 less opaque ; but it must be observed that these 

 characters require a power of about 100 linear, applied 

 to a portion of the sponge in Canada balsam, to render 

 them distinct to the eye. 



" A few simple oscula were observed in the dermis of 

 the part of the sponge examined. The pores were not 

 detected. 



" The dermal membrane is closely attached to the 

 mass of the skeleton beneath it, and no distinctive 

 spicula were apparent on it. 



" The skeleton is remarkable in its mode of structure. 

 It consists of numerous thin patches of spicula, dis- 

 posed at various angles to each other, and in some 

 parts they are so intermixed as to render their dis- 

 tinctive fascicular characters very doubtful ; and the 

 abundant intermixture of prostrate internal defensive 

 spicula beneath and among them, acids greatly to this 

 confusion. The skeleton spicula are long and very 

 slender, and the number, fasciculated together, vary 



