380 ^Ir. T. Hitrgin o/i a luw HexactlneUid 



spines bent, and all pointing towards one and the same end of 



the spicule ; 5, fusitorni-accratOj sj)arscly .sj)ined throusxljont, 

 but the spines on each half ])(>iiitini;- ri'sjiec'tivi'ly towartl.s the 

 midd/e ot' the spicule (PI. XXI. Ii<^. .•}) ; (>, the laru^c stout, 

 smooth acerate (whose nieasurcuicnts have just been stated), 

 conspicuous from its great size amongst the other forms with 

 which it is associated (PI. XXII. fig. 1) ; 7, slender, smooth, 

 crucial or four-armed spicules, the arms horizontal and at 

 right angles to each other; 8, similar-shaped s})icules, larger 

 than the last named, but barbed harpuuu-like towards the 

 ends of the arms (PI. XXI. lig. 4) ; \), .snudl scxradiate forms 

 furnished with rather long spines, wiiicii counuence about half- 

 way along the rays, shooting out in the direction of their 

 points and bent upon themselves outwards (fig. 5) ; 10, a nail- 

 like fonn with short straight arms and long plumose shaft, sj)ines 

 rather short; 11, large eight-armed birotulates, about l-90th 

 of an inch in length, with dome-shaped lieads and four or eight 

 tubercles, chietlj confined to a ring round the middle of the 

 shaft ; 12, a small eight-anned birotulate of slender fonn, 

 about 1 -225th of an inch in length (fig. 6), the shaft of 

 which is studded throughout with short obtusely pointed 

 spines, the heads not dome-sha])ed but pointed ; 13, a very 

 minute birotulate, averaging 1-I2o0th of an inch in length, 

 having the appearance of bearing only two arnis at each end 

 (fig. 7), but, when carefully focused endwise, is .seen to be 

 multihamate, the normal number of its arms being probably 

 eight, though in some instances six only can be counted, whilst 

 in others ten may be seen, the shaft spined more or less 

 throughout, and the heads dome-shaped ; this minute spicule 

 is found in great numbers in the dermal sarcode, as well as 

 generally throughout the sponge. 



The long fusiform-acerate spicules form the fibrous lines of 

 the general structure, on which are seen the large birotulates 

 and the long-shafted plumose forms ; whilst the crucial s])icules 

 are found in the sarcode of the walls of the canals. ]\Iost of 

 the acerate forms are of the sexradiate type, as is evident from 

 the cross in the central canal in the middle of the spicule ; but 

 the main shaft only is produced, the arms either not being 

 produced at all or appearing only as tubercles. 



The spicules of the sponge immediately embracing or sur- 

 rounding the glass rope where it issues from the mass are 

 several varieties or modifications of the sexradiate tyY>e. There 

 is no Polype on the rope, nor any membranous covering of any 

 kind. The .sponge-head is grooved inwards circuhirly round 

 the rope, as a pear often is round the stalk ; and the plumose 

 spicules of the dermal latticework can be traced close up to the 



