130 Mr. H. J. Carter on two HexactinelUd Sponges. 



of the last species, as tlie illustrations figs. 7 and 14 respec- 

 tively, which are drawn to the same scale, indicate) and nu- 

 merous, particularly towards the surface ; and the little bundles 

 of minute undulating, fine, hair-like acerates (fig. 10, g)^ which 

 I have so often figured in the Esperiadge and other sponges of 

 the Holorhaphidota, are also very plentiful, and very frequently 

 present a distinct, tricurvate or bow-like form (fig. 15). 



I need not allude further to the differences between this and 

 the foregoing species, viz. Eurete farreopsis^ as these may be 

 gathered from the descriptions and illustrations respectively. 



In the formation of the lanterns from the sarcodic substance 

 one cannot help being struck with the fact that, while this 

 part of the sponge appears to be Radiolarian, the addition of 

 the Spongozoa makes the sponge. This " radiolarian " sarcode 

 is the " intercellular substance, which forms the bond of 

 union between the cells " in sponges, that I described and 

 delineated in Spongilla in 1849 (Ann. & Mag. Nat. Hist. vol. 

 iv. pp. 87 and 91, pi. iv. fig. 2) as possessing the polymor- 

 phic power and contracting vesicles of an Amoeba. 



EXPLANATION OF PLATE IX. 



Fig. 1. Eurete farreopsis, n. sp., natural size ; from a pliotograph. 



Fig. 2. The same. Five diagrams, to show the mode of growth, com- 

 mencing with a, simple cylinder with circular orifice ; b, the same, 

 with orifice expanded ; c, the same, with orifice become funnel- 

 ehaped ; d, with orifice elliptical and contracted in the centre, 

 like the figure 8 ; e, approximated sides united so aa to form a 

 simple cylinder on each side, with circular orifice, //, like that 

 of a. 



Fig. 3. The same, minute structure of the wall, magnified, aaaa, fibre ; 

 h h b b, knots or points of junction of the fibre ; c c c, occasional 

 spines on the same ; d d, minute hexactinellid spicules which the 

 fibre has attached to itself: e, scopuline spicule ; /, small rosette, 

 common form ; g, large rosette, occasional form. Scale l-24th 

 to l-1800th inch. 



Fig. 4. The same, form of staple sexradiate spicule. 



Fig. 5. The same, spined acerate. 



Fig. 6. The same, scopuline spicule, a, shaft ; 6, arm ; c, bead of arm, 

 more magnified, to show the form and arrangement of the spines. 



Fig. 7. The same, usual form of the rosette. (The third axis, which 

 would be vertical to the others, has been omitted for perspicuity.) 

 N.B. Figs. 4 to 7 inclusively are on the scale of l-24th to 

 l-6000th of an inch. 



Fig. 8. Myliusia Grayi, Bk., natural size ; from a photograph. 



Fig. 9. The same : four knots or trapezoids, magnified, to show their ear- 

 liest appearance, a, trapezoid ; b, reticulated threads of silici- 

 fying sarcode extending from point to point of the sexradiate 

 spicule, c. (The vertical axis of the latter omitted here also 

 for perspicuity.) 



Fig. 10. The same : four knots or trapezoids, magnified, to show their 

 form under full development, a, trapezoid with reticulated 



