544 GILBERT 0. B0UHN13. 



EXPLANATION OF PLATES 40—43. 



lUustnitiug Mr. (Jl. C. Bourne's paper on " The Structure and 

 Eormatioii of the Calcareous Skeleton of the Anthozoa." 



PLATE 40. 

 I'los. 1 — 5. — A loyoiiiiim (lij,M(,iil,uin. Zeiss, ^\ lioiii. iimii., c. oc. 8. 

 Fig. I. A f^roiii) of sclcioblusUc cells Iroiii tlic biisc ol ;i polyp, scl. A 

 small sch'rilo in course oi" i'oniiiitioii enclosed in a vacnole in the 

 seleroblasl,. oo. Ovoid l)odics. ffr. Finely i,M'annlar cells wliicli pro- 

 bably form mesof^lica. 

 Kij;. 2. A scleroblast enclosinf^ a liirp;cr sclorito ; the cytoplasm is still 



abundant, and contains i^^ranules and vacuoles. 

 Fig. 3. A larger scUsrile enclosed in a scleroblast. 

 Fig. I'. Two twin-sclerites enclosed in a twin cell with two nuclei. 

 Fig. 5. A cliaracteristic spicule enclosed in a tliiu protoplasmic envelope 

 with two nuclei. 

 Fid. ('». — A single scale-like spicule of riumarella delicatissima, 

 Wright and Stiidcr. Zeiss i{, oc. 4. 



Fi(i. 7. — The same spicule viewed through the polariscope, showing the 

 dark cri»ss due U) the extinction of light, by those component, crystals whose 

 optic axes lie in four positions ut right angles to ouc another. Zeiss It, oc. 2. 

 Figs. S — 12. — ISpongodes, sp. F 



Fig. S. A single spicule Irom the stem, showing the warty projections 



and the dark axial con;, (tu\ 

 Fig. U. A. transverse section of a similar si)iculi', showing (r.r., the axial 

 core; ra., the radial cords, nnuiy of which are bifurcated; <'■//., the 

 concentric lines of growth. 

 Fig. 10. A longitudinal section of a similar spicule, showing me., the 

 medullary portion; in. p., the intirmeiliale portion; and co. p., the 

 cortical portion; the other lettering as in l''ig. i). 

 Fig. II. Fart of a longitudinal section through a spicule wliieli has been 

 crushetl after grinding. The straiuls of iibro-crystals are clearly seen, 

 traversed by the radial cords, fu. 

 Fig. 12. I'art of a spicule which has been carefully decalcilied with weak 

 acetic acid. t/i(/. IJemains of mesughva. s/i. Spicular sheath, or. r. 

 Core composed oi intetlacing organic threads, or. ra. Itadial organic 

 threads corresponding to the radial cords in Figs. 'J and 10. 



