SPONGES.-HALLMANN. 



213 



to deep brown ; the darker colour is due to the presence of 

 pigmented cells. In some specimens an exceedingly thin 

 dermal membrane is visible on the less exposed parts. 



The main skeleton is an irregular small-meshed reticula- 

 tion of well-developed pale horny fibres, the stoutest of which 

 may attain a diameter of 100 ;<. 

 The main fibres are provided 

 with a somewhat meagre, dis- 

 crete, semi-plumose spicular 

 core which comprises both 

 principal (stylote) and auxiliary 

 (subtylostylote) megascleres ; 

 the connecting fibres are 

 destitute of contained spicules, 

 but, like the main fibres, are 

 rather scantily echinated by 

 slender accessory acanthostyles. 

 The principal styli of the main 

 fibres are, in general, set more 

 or less obliquely to the direction 

 of the fibre, sometimes at such 

 an angle that they become, in 

 effect, echinating spicules. On 

 the outer aspect of the super- 

 ficial transverse fibres, echinat- 

 ing principal styli occur in con- 

 siderable number ; in this situa- 

 tion they stand quite perpen- 

 dicularly to the fibre. Between 

 the principal and accessory 

 spicules, however, it is impos- 

 sible to draw a hard and fast 

 line of separation, since — 

 although the transition between 

 them is fairly abrupt — the one 

 form graduates into the other. 

 The interstitial spicules are 

 auxiliary subtylostyli and toxa, 

 together with occasional prin- 

 cipal and accessory styli ; the 

 toxa are fairly plentiful in the 

 deeper parts, but become par- 

 ticularly abundant in the imme- 

 diate neighbourhood of the sur- 

 face. The dermal membrane contains a few horizontally 

 disposed auxiliary spicules and numerous scattered toxa 

 Chelae are absent. 



Fig. \'h — ClatIiyia caelata. a 

 Principal style. b Avixiliarj' 

 style. c Acanthostyles. d 

 Toxa. 



