212 CEYLON PEARL OYSTER REPORT. 



(about 0"8 millini. apart, from apex to apex), from the summits of which fine ridges 

 radiate into the intervening valleys, where they branch and anastomose with one 

 another, so as to give rise to a delicate reticulation which is scarcely visible to the 

 naked eye, and in the meshes of which the dermal pores are situate in small groups. 



The colour of the surface in spirit is black, paling to grey below and internally, and 

 the texture compact, but compressible and very elastic. The specimen thus described 

 measures about 90 millims. in height bv 73 millinis. in greatest breadth. Another 

 somewhat similar spirit specimen has been photographed for me by Professor Herdman, 

 and is represented, about two-thirds natural size, in Plate XIV., fig. 3. 



Professor Herdman has also sent me part of the macerated skeleton of a much 

 larger specimen. The piece sent is a segment of what appears to have been a massive, 

 hemispherical sponge, with very strongly convex upper surface and broad flattened 

 base. Numerous large vents, up to 8 millims. in diameter, are scattered singly over 

 the upper surface, each at the end of a long, vertical oscular tube. Between these 

 vents the surface is rather uneven (but not channelled or grooved) and honeycombed 

 by close-set narrow vertical canals (inhalant) about 0"5 millim. in diameter, which 

 reduce the skeleton reticulation to a mesh-work of thin trabecular which terminate at 

 the surface in small, slightly projecting villi. The texture, after soaking in water, is 

 very soft and elastic and not very tough, and the colour is pale greyish-yellow. The 

 specimen from which this piece was taken must have been about 200 millims. in 

 diameter by 100 millinis. in height. 



The primary fibres of the skeleton (Plate XVI., fig. 5) run parallel with one another 

 (at distances of about - 8 millim.) towards the surface, where they end singly in the 

 conuli. They rarely branch, and apparently never anastomose. They are about 

 0"04 millim. in diameter and composed chiefly of broken sponge spicules, with 

 comparatively little spongin cementing them together. They are connected with one 

 another by a polygonal-meshed network of secondary fibres, in which the meshes vary 

 greatly in size and shape, while the fibres are of fairly uniform diameter and only 

 rarely contain foreign matter. Average diameter of meshes, say, about - 17 millim. ; 

 diameter of the secondary fibres themselves, when fully developed, about 0"02 millim., 

 but often less. 



Owing to the quantity of broken spicules which they contain, the primary fibres 

 are distinctly visible to the naked eye in the macerated sponge, appearing as very 

 fine threads of a paler colour than the rest of the skeleton, and thus constituting what 

 is perhaps the most obvious distinctive feature of the variety. 



The dermal membrane contains numerous broken sponge-spicules scattered 

 through it. 



In internal anatomy this variety agrees minutely with Schulze's classical account 

 of the bath sponge (72), so that it is unnecessary to describe the canal-system and 

 histology in this place. One point perhaps deserves mention, and that is the very 

 strong development of long bands or cords of granular fibrous cells, running through 



