48 THE VOYAGE OF H.M.S. CHALLENGER. 



Sponge an irregular tuberose on subglobose framework, composed of anastomosing 

 lamellar branches. These are covered by a silvery dermal membrane, easily detached 

 from the spongy medullar mass. Pseudo-skeleton composed of different xenophya, 

 principally sponge spicules, Globigerina shells, and mineral particles. 



Cerelasma lamellosa is represented in the Challenger collection by two tolerably well- 

 preserved specimens, the smaller subglobose, 7 to 9 mm. in diameter, the larger more 

 irregular, tuberose, 16 to 20 mm. in diameter. The coarser and finer structures are the same 

 in both. The body appears to the naked eye as a rather massive framework, composed of 

 irregular lamellar branches, the thickness of which is 1 mm. on an average (the thickest 

 branches 1"5 to 2 mm., the thinner only 0"6 to 0'8 mm.). The lamellar branches are so 

 united as to form an irregular network of inter-canals or of anastomosing tubes, which 

 are invested by the silvery dermal membrane. These curved inter-canals are for the 

 most part cylindrical, with a diameter of 1 to 2 mm., rarely more. 



The dry sponge is not elastic, rather firm, but friable. The whole surface and all the 

 inter-canals are silvery, covered by the whitish cortex or dermal membrane, whilst the 

 transverse section of the medullar mass of the lamellar branches is brown, partly 

 yellowish, partly blackish, densely porous (fig. 6). After treatment with carmine the 

 cortex becomes rose, the medidla blackish purple. 



Dermal Membrane. — The thin silvery dermal membrane, which covers the whole 

 surface of the anastomosing branches, and also lines all the cavities between them, may 

 be easily detached from the soft brown medullar mass. Its white opaque appearance is 

 produced partly by Globigerina shells and their fragments, partly by other xenophya 

 taken from the surrounding ooze, partly by very small roundish mineral particles, 

 which are not soluble in mineral acids. The whole dermal membrane is densely pierced 

 by circular pores, which are very distinct in this species. Between the pores of the 

 sponge are visible larger scattered openings, the external mouths of the tubes of the 

 symbiotic Hydroid. 



Medullar Substance. — The brown main mass of the sponge or the porous medullar 

 substance, which remains after the detachment of the white cortex, is composed of the 

 transparent maltha and of a dense network or framework of anastomosing horny 

 lamellae, both overladen with xenophya, and further of a loose network of the symbiotic 

 Spongoxenia. The structure of the narrow irregular canal-system, and especially the 

 shape of the flagellated chambers, could not be made out in a satisfactory manner, but it 

 seems to be similar to that of Siwngelia. 



Spongin-Skeleton. — The horny lamellae of the true skeleton are in general thin and 

 broad, of a yellow colour, very irregularly branched, varying greatly in thickness and 

 breadth. They pass over immediately into the horny substance of the saccular envelopes 

 which surround many xenophya. The lamellar branches are everywhere connected by 

 anastomoses, and form a dense framework, the meshes of which are filled up partly by 



