STUDIES IN SPICULE FORMATION. 53 



6. LoEWiG and Kollikee. — "De la composition et de la Structure des En- 



veloppes des Tuniciers," 'Ann. Sci. Nat.,' 3rd ser., t. v, 1846. 



7. Pbuvot. — " Sur I'organization de quelques Neomeuieus des cotes de 



Trance," ' ArcL. Zool. Exp.' (2), ix, 1891. 



8. TuiELE, J. — " Beitrage zur Vergleichenden Anatomic der Amphineuren," 



'Zeit. f. wiss. Zoologie,' Bd. Iviii, 1894. 



9. WiKEN. — " Studien iib. die Solenogastres," I and II. ' Svenska vet. Akad. 



Handl.,' xxiv, xxv, 1892-93. 



10. Woodland, W. N. E. — " Studies in Spicule Formation. I. Sycon 



Sponges," 'Quart. Journ. Micr. Sci.,' vol. 49, 1905. 



11. " Studies in Spicule Eormation," V. 'Quart. Journ. Micr. Sci.,' 



vol. 51, 1907. 



EXPLANATION OF PLATE 5, 



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

 Formation" (VI). 



Figs. 1 and 3, x 640 ; Figs. 3—6, x 192 ; Figs. 7—18, x 1280. All drawings 

 were made with the camera lucida. 



Fig. 1. — Young stages in the development of the mouaxon spicules of 

 Goniodoris castanea. The thick median portion is the first to be formed. 



EiG. 2. — Apparently an abnormal spicule of G. castanea possessing two 

 thickened club-like extremities and two nuclei, and so somewhat resembling a 

 young alcyonarian spicule. 



Figs. 3 and 4. — Older spicules of G. castanea, each entirely enveloped in 

 cell-substance and with one nucleus. 



Fig. 5. — Small monaxon spicules of Archidoris tuberculata. These 

 spicules possess no central thickening and have small spherical nuclei. 



ElG. 6. — Small (young) spicule of Lamellidoris bilamellata; large 

 type of spicule, and usually possessing a median spine. 



Figs. 7 and 8. — Young spicules of Proneomenia aglaophenise. 



Figs. 9 and 10. — Older spicules of the same. 



Figs. 11 and 12. — Young spicules of Dondersia banyuleusis. 



Fig. 13. — Older spicule of the same. 



Figs. 14 — 18. — Stages in development of the stellate spicules of Lepto- 

 clinum commune. 



