222 -ENDEAVOUR" SCIENTIFIC RESULTS. 



reticulation of fairly stout fibres with well-marked differences 

 in spiculation between the main and connecting fibres ; 

 whereas, in regions of least density, it is a very loose reticu- 

 lation of fine fibres, and the main fibres, in point of stoutness 

 and spiculation, are but slightly distinguished from the con- 

 necting. 



Echinating acanthostyles are irregular in occurrence, and, 

 on the whole, comparatively scarce ; they are sometimes com- 

 pletely enclosed within the fibres. Principal and auxiliary 

 spicules, the former in greater number, are somewhat spar- 

 ingly scattered between the fibres, and with them occur also a 

 few acanthostyles. A notable proportion of the "extrafibral" 

 principal styli are disposed perpendicularly to the fibres in 

 such a way that they appear to echinate the fibres ; on careful 

 examination many of these prove to be ensheathed in an ex- 

 ceedingly thin layer of spongin continuous with that of the 

 fibre, but very few indeed are actually imbedded in the fibre. 

 A further point worthy of notice is the fact that the interstitial 

 and quasi-echinating principal styli (like those, already men- 

 tioned, which form the superficial fibres) are, in general, much 

 stouter than those \\'hich core the longitudinal main fibres. 



The dermal menjbrane contains numerous horizontally dis- 

 posed scattered auxiliary spicules. These are not so abundant 

 as to give rise to a visible incrustation in the dry state of the 

 sponge. 



Megascleres. — 



(i.) The principal styli are typically straight subfusiform 

 spicules, often with a slight w^aist-like sub-basal con- 

 striction. They are usually quite smooth, though a 

 verv appreciable proportion, particularly among 

 those of intermediate and lesser length, carry a few 

 low spines at or near the basal end. Their maximum 

 size is 1 60 X 10 p. Spicules below a length of 120 ji 

 are rare and usually bear a greater or less number of 

 spines scattered over their whole length ; amongst 

 these shortest spicules are some which, in form, 

 bridge over the gap between the principal and acces- 

 sory spicules, 

 (ii.) The accessory acanthostyles are sub-conical spicules, 

 provided over their whole length with small spines. 

 They vary in length from 55 to over 100 n \ but in- 

 dividuals of greater size than 70 x 6 j! are rather 

 rare, and usually show a reduced spination. 



(iii.) The auxiliary spicules are straight subtylostyli, 

 sometimes basally tipped with a minute spination ; 

 size 120-170 X 3.5 p. 



