SPONGES.-HALLMANN. 



157 



tough, and when dry forms an obscure whitish incrustation; 

 in alcohol it is translucent and of light greyish colour. Beneath 

 the membrane, the sponge is dull yellow. The texture is much 

 looser and the consistency much softer than in the varieties 

 arcmicea and levis. In a dry state the consistency varies ac- 

 cording to the extent to which the sarcode has been removed, 

 from firm, yielding to pressure and slightly brittle, to soft, 

 spongy and elastic. 



The main skeleton consists of exceedingly tortuous branch- 

 ing fibres running longitudinally. In the deeper parts they 

 might almost be described as 

 curled, but towards the surface 

 they straighten out somewhat, 

 though still remaining sinuous. 

 The spicular axis of the fibres, 

 •consisting of oxea only, is sur- 

 rounded by a thick sheath of 

 . transparent spongin in which 

 the echinating spicules are 

 deeply imbedded with their 

 bases quite in contact with the 

 spicules of the core. The wind- 

 ing courses which the fibres 

 pursue, result in the frequent 

 crossing and apposition of ad- 

 joining fibres, and where con- 

 tact occurs connections are fre- 

 quently formed by the fusion of 

 their spongin-en\ elopes. There 

 are no proper connecting fibres, 

 though occasionally the union 

 of fibres in the manner des- 

 cribed produces the appearance 

 of such. The fibres might be 

 said to form a pseudo-reticula- 

 tion, in which the meshes are 

 for the most part of elongated 

 form. In sections prepared ^ostyle?^'" 

 from dry specimens it is seen 



that the spongin — or what appears to be spongin — in 

 addition to its envelopment of the fibre-spicules, extends 

 as thin films or membranes between the fibres, dividing 

 the interior of the sponge into incomplete compartments, 

 as it were. The interstitial spicules, consisting of acantho- 

 styles and oxea in about equal number, appear to be entirely 

 restricted to these membranes. The echinating spicules are 

 never so abundant as to obscure the axial spicules. 



Fig. 28 — Crella incrustans var. 

 digitata. a Oxea. b Principal 

 c Dermal acan- 



