DESMACIDON. 181 



of the dermis from the opposite end of the sponge and 

 examining them, as I had the first specimens mounted, 

 the mystery was at once solved ; the characteristic 

 tissues of Baphiodesma were entirely absent, and the 

 sections under examination exhibited all the characters 

 of a pure and simple specimen of Desmacidon cegagro- 

 pilits ; and I became assured that the intermixture of 

 tissues was partial, and existed only at one portion of 

 the specimen. A thin section from the basal portion 

 of the sponge afforded precisely the same evidence as 

 the sections last described. 



" The occurrence of the intermixture of these two 

 species, from the close similarity of portions of the 

 component parts of their respective bodies, is exceed- 

 ingly interesting and instructive. The skeleton of the 

 two species are both f usiformi-acuate, and the bihamate 

 retentive spicula of each are exactly alike in form and 

 in their abundance on the membranous tissues of each, 

 so that it required no small share of experience of 

 sponges to detect this remarkable mixture of structure. 



" The beautiful rosette-shaped groups of the charac- 

 teristic spicula of Raphiodesma lingua afforded an 

 excellent clue to the solution of the mystery, and the 

 contrast between the structures of the dermal membranes 

 was also very decisive ; while the dermal spicula of D. 

 cegagropilus are slender and irregularly dispersed, those 

 of R. lingua are stout and fasciculated, forming an 

 irregular network. I ultimately succeeded in detaching 

 a very characteristic fragment from the surface with 

 a few of the fasciculi of the skeleton of R. lingua 

 beneath it, without any portion of the structures of 

 the Desmacidon. From all these appearances it is 

 evident that the Raphiodesma lingua was in a very 



