652 



REVISION OF THE AXINELLIDiE, 111., 



flocculation (consisting mainly of separate spicules); occasionally, 

 however, b}^ the exercise of especial care, one succeeds in obtain- 

 ing, as pai't of the residue, small masses of coherent skeleton. 

 From examination of these, the skeleton, which is extremely 

 scanty, is seen to consist partly of slender, multispicular (main) 

 fibres running irregularly through the sponge, branching and 

 occasionally anastomosing as they go, and partly of a very sparse 

 and irregular reticulation of single spicules and short pauci- 

 spicular fibres extending between the main fibres and partly 

 serving to connect them (PI. xliv., fig. 4); the structure is much 

 less dense than would appear from the figure, inasmuch as in the 

 mounted preparation, from which the photograph was taken, the 

 skeleton has been compressed under the cover-glass to less than 

 half its original thickness. The main fibres are rarely as much 

 as 40// in stoutness, and are composed of fairl^T^ closely-packed 

 spicules, directed longitudinally, and barely held together by an 

 evanescently small amount of hyaline spongin, which becomes 

 discernible only when stained. Outside the main fibres, spongin 

 is generally wanting; but here and there, where several spicules 

 cross one another at a point, a faint investment of cementing 

 substance is sometimes detectable. 



In ordinary sections of the sponge (i.e., with the fieshy tissues 

 intact) the precise pattern of the skeleton is usually not manifest: 

 for, in thick sections, it is generally more or less obscured in 

 consequence of an opacity due to great numbers of pigmented 

 granules scattered everywhere through the tissues ; while, in 

 thinner sections, owing to the sparseness and irregularity of the 

 skeleton, the main fibres are usually more than once cut across, 

 and thus appear not to be continuous, and the intermediate 

 skeleton appears to consist merely of a few scattered spicules. 

 Trichodragmata occur rather abundantly through all parts of the 

 interior, but are not very noticeable owing to the obscuring 

 effect of the pigment-granules and the extreme slenderness of 

 the individual trichites. Singly scattered trichites are scarce. 

 The spined microxea likewise occur in all parts of the .sponge, 

 but are nowhere abundant ; they are most numerous in the 

 dermal membrane. 



