108 Proceedings of the Royal Physical Society 



(S) Lankester, E. R. — Observations on the Development of the Cephalopoda. 



Q.J. M.S., xv., 1875. 

 (9) Steenstrup, J. — Zur Orientirung iiber die embryonale Entwicklung 



verschiedener Cephalopodentypen, Biol. Centr., ii., 1882/1883. 



(10) Teichmann, E. — Die friihe Entwicklung der Cephalopoden, Verh. d. 



Deutscheti Zool.Ges., 1903. 



(11) Ussov. — Nadliudenia nad razvitiem golobonogich molliuskov. Moscow, 1879. 



(12) Vialleton, L. — Recherches sur les premieres phases du developpement de 



la seiche (Sepia officinalis), Ann. Sci. Nat. (7) Zool., t. vi., 1888. 



(13) Watase, S. — Observations on the Development of Cephalopods. Homology 



of Germ-Layers. Johns Hopkins Univ. Circ, vi., 1888. 



(14) Watase, S. — Studies on Cephalopods: I., Cleavage of the Ovum, Journ. 



o/Morph., iv., 3, 1891. 



(15) Wilson, E. B. — The Cell in Development and Inheritance. 2nd ed., N.Y., 



1900. 



Explanation of the Figures. 



[Figures 1-23 were drawn by E. A. M. with the camera lucida and Zeiss oc. 2, obj. B. ; the 

 enlarged drawings of the polar bodies with Z. oe. 4, obj. D. Figures 24-30 were drawn by J. H. K. — 

 fgg. 24-26 with Z. oc. 2, obj. B.; fgg. 27-29 with Z. oc. 4, obj. A.; fgg. 30-31 with Z. oc. 2, obj. D.] 



Fig. 1. 2 blastomeres. Nuclei resting. (3 polar bodies). 



Fig. 2. 2 blastomeres. Nuclei dividing. 



Fig. 3. Ditto. 



Fig. 4. 4 nuclei. Indication of second cleavage furrow. 



Fig. 5. Ditto. Slightly advanced. 



Fig. 6. Second cleavage furrow formed. 



Fig. 7. 4 blastomeres. Nuclei resting. 



Fig. 8. 4 blastomeres. 2 nuclei resting, 2 dividing. 



Fig. 9. 4 blastomeres. 4 nuclei, dividing. 



Fig. 10. Formation of 8 blastomeres. 



Fig. 11. 8 blastomeres. 8 nuclei, resting. 



Fig. 12. Formation of 16 blastomeres. 12 nuclei resting, 2 dividing. 



Fig. 13. Formation of 16 blastomeres, advanced. 



Fig. 14. Ditto. 



Fig. 15. 16 blastomeres. 16 nuclei, resting. 



Fig. 16. 16 blastomeres. 8 nuclei resting, 8 dividing. 



Fig- 17- „ „ 4 „ „ 12 „ 



Fig- 18- „ „ 2 „ „ 14 „ 



Fig. 19. „ „ 16 „ dividing. 



Fig. 20. Formation of 32 blastomeres. 



Fig. 21. Ditto, advanced. 



Fig. 22. Ditto. 



Fig. 23. Blastoderm. 



Fig. 24. Ditto. 



Fig. 25. Formation of " autoplasts." 



Fig. 26. Ditto. 



Fig. 27. Transverse section through blastoderm. 



Fig. 28. Ditto. 



Fig. 29. Ditto. 



Fig. 3d. Ditto. 



{Issued separately ', Jane 2, 1910.) 



