42 W. WOODLAND. 



Literature. 



1. Agassiz, a. — 'Bull. Mus. Comp. Zool. HarvaiJ/ vol. x, 1882. 



2. Fewkes, J. W.— Op. cit., vol. xii, 1885. 



3. Op. cit., vols, xiii (1886) and xvii (1890). 



4. LuDWiG, H. — ' Holotbuiien der Hamburger Magalhaensischen Sammel- 



reise,' Lief, iii, 1898. 



5. 'Zool. Jabrb.,' Suppl. 4; 'Fauna Cbilensis,' Heft, iii, 1898. 



6. 'Fauna Stat. Neapel,' xxiv, 1897. 



7. 'Zeitscbr. f. wiss. Zool.,' vols, xxxiv (1880) and xxxvi (1882). 



8. MoRTENSON, T. — 'Medd. Gronland,' vol. xxix, 1903. 



9. Seeliger, O.— 'Zool. Jabrb., Abtb. f. Morpb.,' vol. vi, 1893. 



10. Semon, R.— 'Mittbeil. Zool. Stat. Neapel,' vol. vii, 1887. 



11. Theel, Hj, — 'Nova Acta R. Soc. Sci. Upsala,' ser. iii, 1892. 



12. 'Bib. Svenska Akad. Handl.,' vol. xxviii, ser. 4, 1902. 



13. Woodland, W. — "Studies in Spicule Formation" (I — IV), 'Quart. 



Journ. Micr. Sci.,' vol. 49, 1905—1906. 



EXPLANATION OF PLATES 3 and 4, 



Illustrating Mr. W. Woodland's " Studies in Spicule 

 Formation" (V). 



Fig. 1 drawn natural size; Figs. 2, 3, 8, 9, 14, 15, and 23 X 1280 dia- 

 meters; all otber figures X 640 diameters. All figures (save Fig. 1) drawn 

 vyilb tlie camera lucida. 



PLATE 3. 



Development of tlie plate spicules of Ampbiura elegans (Figs. 1 — 7), 

 Opbiotbrix fragilis (Figs. 8 — 13), and Ecbinus esculentus (Figs. 

 14—18). 



Fig. 1. — Young Ampbiura in wbicb the spicules were observed. (Several 

 specimens of Ampbiura were considerably smaller than tbose bere depicted.) 



