BY :■{• F. KALLMANN. f)25 



while the average distance apart of the main fibres is not less 

 than "-'OO/x. As the main fihi-es trend surfacewards, - with 

 gradually increasing deflection from the longitudinal direction 

 as they proceed, they increase in number, mainly by branching, 

 but partly also (at least in proximity to the surface) through the 

 formation of additional ones which take origin from connecting 

 fibres; and they arrive at the surface almost at right angles. 

 The spicules of the main fibres are seldom more than 4- or 5-serial 

 in their arrangement, very rarely as many as 9- or 10-serial; as 

 a rule they lie fairly closely together, forming a moderately 

 compact core. The most superficially situated fibies of the 

 skeleton, including the outermost of the connecting fibres, give 

 support to relatively numerous outwardly-directed spicules, for 

 the most part collected, or tending to be collected, into loose 

 divergent tufts surrounding the extremities of the main fibres. 



In balsam-mounted sections of the perfect sponge {i.e., with 

 the soft tissues intact), the above-described features of the 

 skeleton are to a very considerable extent obscured or di.sguised. 

 This is due partly to the very pale colouration of the spongin, — 

 in consequence of which tlie outlines of the fibres are usually 

 almost or quite indiscernible,— and partly to the fact that the 

 bulk of the megascleres are located externally to the fibres. 

 These extra-fibral megascleres for the most part are not scattered 

 irregularly through the mesogloea, but are situated chiefiy in 

 proximity to the main fibres, lying in approximate parallelism 

 therewith. As a consequence, it is often diflicult. or even im- 

 possible, to distinguish between spicules lying immediately 

 adjacent to the fibres and others enclosed within them; and the 

 skeleton may thus appear as if composed solely of spicules, for 

 the most part directed parallelly to the directions of growth of 

 the sponge, and more or less collected loosely into ill-defined 

 sti'ands. Irregularly scattered megasclei'es also are present, as 

 well as relatively few transversely-directed ones, the latter of 

 w^ich always occur singly. Sigmata and trichodragmata are 

 present in moderate number, but the former are not readily 

 perceived owing to their slenderness ; rare singly-scattered 

 trichites also occur. 



