112 CEYLON PEARL OYSTER REPORT. 



Owing, on the one hand, to the enormous quantity of foreign matter adhering to 

 the surface, and, on the other, to the great size of the megascleres, which interfere 

 greatly with the cutting of thin sections, the investigation of the canal system of this 

 sponge is attended with exceptional difficulties, and I have come to no satisfactory 

 conclusions on the subject. 



One of the most striking features of the sponge is the dense fibrous layer of the 

 ectosome, which, when the sponge is cut in half, is conspicuous even to the naked eye 

 as a white layer about 0"4 millim. thick, dividing the body into inner and outer 

 portions, and forcibly calling to mind the similar layer of fibrous tissue in Stelletta 

 herdmani. This dense fibrous layer consists of bundles of fine fibres closely matted 

 together and running in all directions. It does not, perhaps, form quite the 

 innermost portion of the ectosome, for beneath it lies a thin gelatinous layer containing 

 subcortical crypts, from which the inhalant canals of the choanosome probably take 

 their origin. 



The outer layer of the ectosome varies much in thickness. It is partly 

 collenchymatous, consisting of a clear gelatinous matrix with an immense number of 

 large granular stellate cells embedded in it, and partly fibrous, the fibrous condition 

 being apparently arrived at by elongation of similar cells in a direction parallel to the 

 surface. Roughly speaking, this fibrous tissue may be said to occur between two 

 layers of the collenchyma, but the two kinds of tissue are not sharply differentiated 

 from one another, and the fibrous layer is not nearly so well defined or so dense as 

 the inner fibrous layer already described. The outer layer of the ectosome alone 

 takes part in the formation of the finger-like projections on the surface of the sponge, 

 the inner fibrous layer not being continued into these. 



The choanosome is rather compact and finely granular, but, owing perhaps to want 

 of penetration by the preserving medium, my sections do not enable me to make out 

 details of the histology or the arrangement of the flagellate chambers. 



RN. 62 (Gulf of Manaar). 



Family : TETHYID^. 



Astromonaxonellida with stylote megascleres and euasters for microscleres ; with 

 strongly developed fibrous cortex and radially arranged skeleton. 

 I have discussed the probable origin of this family in speaking of the genus 

 Cryptotcthya. 



Tethya, Lamarck. 



More or less spherical Tethyidas, without highly specialised pore-bearing grooves and 

 without a sand-layer in the choanosome. 



Tethya lyncurium, Lin. 



There are in the collection a number of specimens of Tethya which have given me a 

 great deal of trouble as regards their collect nomenclature. 1 have finally decided to 





