260 PLATE LXXXI. 



smooth inner or exhalent one with its numerous oscular 

 perforations. 



Microscopically examined, the outer and inner mem- 

 branes of the surfaces of the cup are in very strong 

 contrast. The former is furnished with a stout poly- 

 spiculous reticulation, in the areas of which the pores 

 are situated. The rete is remarkable in its structure ; 

 it appears to consist of primary and secondary lines ; 

 the first are stout polyspiculous bundles, sometimes 

 running parallel to each other, but not always coin- 

 ciding in their direction ; the secondary lines are 

 formed of single spicula of the same size and form, 

 placed diagonally or at right angles to the primary 

 fasciculi, or of groups of small tension spicula mixed 

 with numerous retentive ones. In the exhalent surface 

 we observe no such reticular structure ; the whole 

 surface is covered with an irregular mixture of large 

 and small tension spicula, felted together as it were, 

 amidst which innumerable stellate, retentive spicula 

 are disposed. 



The exhalent surface of the sponge abounds in large 

 intermarginal cavities immediately beneath the dermis, 

 and on their dermal surfaces there are a considerable 

 number of connecting spicula with their triradiate heads 

 firmly cemented to the inner surface of the membranes, 

 and their shafts projecting into the cavities beneath. 



The normal form of the connecting spicula is that of 

 an expando-ternate one with a very short shaft, and 

 greatly produced radii as represented in Plate LXXXI, 

 fig. 5 ; but these are few in number compared with the 

 abnormal forms, which are exceedingly variable, a few 

 of which are represented by Figs. 6, 7, and 8 in the 

 same plate. 



This surface of the sponge presents a somewhat 

 scattered hispidation, arising apparently from an irre- 

 gular protrusion of the large dermal spicula through 

 the dermal membranes ; but it is very probable that in 

 the living state this character would not be observable, 

 nor does it appear on the inhalent surface of the 



