426 REVISION OF THE MONAXONID SPONGES, iii., 



jacent to it, that the core becomes stouter with age; for one 

 finds, in the older portions of the sponge, that the core consists of 

 an outer (secondarily formed) layer composed of fairly closely 

 packed oxea, and of an axial region which is differently constituted. 

 In spite of the increase in size of the core, no appreciable reduc- 

 tion occurs in the width of the layer extending between it and the 

 surface, nor does there seem to be any marked diminution in the 

 number of the scattered spicules. The axial or first-formed region 

 of the core, as seen in sections of an appropriate thickness, ex- 

 hibits a structure very similar to that figured by Vo8maer(52) 

 in illustration of the skeleton of the type-species of Axinella. It 

 consists of: (i.) numerous longitudinally-running, and interlacing, 

 multispicular fibres (''funieles"), which are similar in character to 

 the already mentioned fibres that run out to the surface, and form 

 a kind of reticulation with narrow eloJigated meshes; (ii.) inter- 

 mingled with these, numerous slenderer diffuse strands, likewise 

 composed of oxea, and usually more or less oblique to the axial 

 direction; and (iii.) singly-occurring elongated flexuous strongyles,* 

 which are interwoven with the fibres. 



Spicules. — In different specimens, one finds differences in the 

 sizes of the spicules, more particularly of the oxea, the differences 

 being chiefly in stoutness and in average length. The maximum 

 length, both of the oxea and the strongyla, appears to be fairly 

 constant; but the relative number of spicules which attain to this 

 varies considerably, and may sometimes be extremely small. The 

 spicules which, throughout the description, have been referred to 

 simply as oxea, include also a number of styli; these styli are 

 usually rare, but, in one of several slides prepared from different 

 parts of the type-specimen, they were met with rather frequently. 

 Variability is shown also in the relative abundance of the 



* Whitelegge(54) says regarding the arrangement of the strongyles that 

 they are "usually disposed at right angles to the columns of oxeote spicules 

 in the main fibres." On the contrary, it seems to be the rule that, lika 

 almost all the other spicules composing the core, they have a more or less 

 longitudinal disposition. 



