Hex ictinellid Spicules and (heir Names. 



349 



in numerous species the holohexasters tend to begone reduced 

 to monohex.istevs which simulate the simple hexactin form. 



xiooo 



Fig. 1. — Scopula of Eurete semperi, F. E. Sell., a holactine monactin 

 with prongs or spines at its central end, but without end-spines at 

 the distal or peripheral end, with axis cross at central end. Ex- 

 amined in glycerine. Camera lucida drawing, x 1000. 



Fig. 2. — Olavula of Farrea occa (Bowerbank), Carter. In glycerine. 

 Camera lucida drawing, x 1000. 



Fig. 3. — Root-tuft spicule of Hyalonema sieboldii, Gray, a holactine mon- 

 actine megasclere. Magnified. 



Fig. 4. — A small hexactin of Eurete semperi, F. E. Sch., welded on to 

 the dictyonal framework. X 350. After F. E. Schulze. 



Fig. 5. — A loose hexactin of E. semperi, F. E. Sch. x 350. After F. E. 

 Schulze. 



Often it is obvious that monohexasters are reduced holo- 

 hexasters, because the end-spine of the former resembles each 



