664 REVISION OF THE AXIXELLID^E, iii. 



exception are regularly sharp-pointed. The full-grown ones 

 (comprising all those ensheathed in spongin as well as the vast 

 majority of the remainder) vary in maximum size in different 

 specimens from 560 x 14/^ to 700 x 18/a, and rarely fall helow 

 350/i in length or below S/i in diameter; interstitially-occurring 

 immature individuals of all sizes down to about 250 x 2/x, how- 

 ever, are to be met with. 



(ii.) Also occurring interstitially, but very scarce (in some 

 specimens exceedingly i-are), are longer and generally less curved, 

 mostly stylote spicules, very frequently more or less blunted or 

 rounded off at the apex and not seldom passing into strongyla, 

 and attaining a maximum size of about 900 x 9/x. Between these 

 and the slenderer forms of the preceding, however, there appears 

 to be a complete series of spicules of intermediate forms and 

 sizes. 



(iii.) The short slender megascleres occurring in loose bundles 

 and also scattered singly in the dermal layer, — which appear to 

 be special dermal spicules, — are slightly curved oxea, frequently 

 blunt-pointed and more or less resembling strongyla, and usually 

 4 or 5//. in diameter and between 250 and 350/x (but ranging 

 from about 200 to upwards of 400/x) in length. They are not 

 distinguishable either in form or size fi'om many of the inter- 

 stitially occurring spicules which appear to be immature forms of 

 (i.) and (ii.). 



Microscleres. — With the exception of a few, which are straight, 

 the acanthoxea are invariably sharply bent at the centre, — the 

 maximum angle of inclination of the actines (which are gradually 

 tapered and sharp-pointed) being about 30°. About 5% of the 

 spicules exhibit a peculiarity in the form of a small bulbous 

 dilatation situated at a short distance (10/x or less) from their 

 mid-point. They range fi'om about 40 to 130/x in length and up 

 to 4 or (rarely) 5/x in diameter exclusive of the spines. The 

 spines are perpendicularly-directed, conical, sharp-pointed, usually 

 very numerous, and scattered irregularly over the whole length 

 of the spicule, gradually decreasing in size towards its extremities; 

 the largest of them are 2 5/x in length. The spicules in their 



