442 



REVISION OF THE MONAXONID SPONGES, iii., 



a rule, no distinction between main and connecting fibres can be 

 drawn. Spongin is developed only in relatively slight amount 

 in the younger parts of the sponge, but later comes to form well- 

 defined fibres (up to 60 /x in diameter) enclosing the spicules and 

 rounding off the angles of the meshes. Many spicules, however, 

 remain uncovered by spongin; and, on the other hand, a small 



Fig. 23. — A xiamon folium. a,Principal oxea, anisoxea, and atyli. 

 a'. Extremities of principal spicules. h, Interstitial stylus. 

 6',Basal extremities of interstitial styli. r, Dermal styli. 



proportion of short fibres are to be found composed entirely of 

 spongin. The spiculation consists almost entirely of the char- 

 acteristic oxea and of unequal-ended derivatives of these (anis- 

 oxea); but here and there, in some parts of the sponge at least, a 

 long slender stylus may be met with: and, in the most superficial 

 layer of the sponge, a very few small dermal spicules occur, lying 

 scattered. The surface is rendered hispid by anisoxea projecting 

 singly or in twos or threes, for three-fourths or more of their 

 length, usually in an obliquely upward direction. 



ASpiciihs. — (a.) The oxea and anisoxea, which range from 180 

 to 420 i-L in length, and up to 2 1 /x in stoutness, are moderately 



