O24 W. WOODLAND. 
17. Sexenxa, E.—‘‘ Keimblatter und Organanlagen bei Echiniden,” ‘ Zeit. 
wiss. Zool.,’ vol. xxxiii, 1879. 
18. Sottas, W. T.—* Tetractinellida,” ‘Challenger Reports, Zool.,’ vol. xxv, 
1888. 
19. Semon, R.—“‘ Beitrage zur Naturgeschichte der Synaptiden des Mittle- 
meeres. I. Mittheilung,” ‘ Mittheil. aus de Zool. Stat. Neapel,’ 1887. 
*“Die Entwicklung der Synapta digitata und die Stammes- 
geschichte der Echinodermen,” ‘Jena Zeit. f. Naturw.,’ Bd. xxii, 1888. 
21. ToEEL, Hs.—‘*On the Development of Echinocyamus pusillus,” 
‘Nov. Arta Reg. Soc. Sci. Upsala,’ Series 3, 1892. 
20. 
22. “ Notes on the Formation and Absorption of the Skeleton in the 
Echinoderms,” ‘ Svensk. Vet. Akad. Forh.’ Stockholm, 1894. 
23. “Preliminary Account of the Development of Echinus 
miliaris,” ‘Bib. Svenska Akad. Handl.,’ vol. xxviii, Series 4, Stock- 
holm, 1902. 
24. Woopianp, W.—* Studies in Spicule Formation,” I. 
25. 
* Studies in Spicule Formation,” II. 
EXPLANATION OF PLATES 18 & 19, 
Illustrating Mr. Woodland’s paper, “Studies in Spicule 
Formation.” III. 
All figures magnified 1000 diameters except Fig. 5 (x 2000) and Figs. 25 
and 26 (x 500). 
PLATE 18. 
Fries. 1—3 show the initial granules deposited in the cells of the longi- 
tudinal strand which is viewed from the surface. 
Fie. 4.—The granule in the longitudinal strand when this latter is viewed 
edge on, as also in Fig. 15. In Fig. 8 the strand is viewed end-on. 
Figs. 4, 8, 10, 11, 12, 15 (and 19 and 20 of Plate 19) show well the pseudo- 
podial processes connecting adjacent cells in the blastoporic ring. 
Fic. 5.—The scleroblast containing the granule, magnified 2000 diameters. 
Fies. 6, 7, 10, 11, 18, 14, 16.—The young triradiates derived from the 
initial granules, 
