DEVELOPMENT OF DISTIOHOPOEA VIOLAOEA. 73 



65. ZiEGLEB., H. E.— "Der biologische Bedeutung der amitotisclie Kern- 

 theilung im Thierreioh," ' Biol. Centralbl.,' xi, 12 and 13, pp. 373— 

 389. Transl. in ' Ann. N. H./ viii, p. 362. 



DESCRIPTION OF PLATE IV, 



Illustrating Dr. Sydney J. Hickson's paper on tlie 

 " Development of Distichopora.^' 



Fig. 1.— Young ovum of Distichopora, situated in the cup-shaped tropho- 

 disc {(r.). The germinal vesicle, G. v., is situated near the centre of the 

 ovum. 



Fig. 2.— Germinal vesicle of the same stage, showing the vacuoles in the 

 nucleolus. 



Fig. 3. — Germinal vesicle of the ovum of Distichopora, migrating from the 

 centre to the periphery. The raembrana limitans becomes obscure over the 

 pseudopodial processes. 



Fig. 4. — A peculiar condition of the germinal vesicle, observed in only one 

 preparation. 



Fig. 5. — A germinal vesicle, with chromatin grannies arranged in a row. 



Fig. 6. — Germinal vesicle, containing numerous minute chromatin granules 

 situated at Ihe periphery of the ovum. 



Fig. 7. — A stage showing the disappearance of the inner part of the mem- 

 brana limitans. 



Fig. 8. — A stage showing the complete disappearance of the membrana 

 limitans. 



Fig. 9.— Section of a young embryo which shows only two large nodes of 

 protoplasm, each of them containing a few deeply staining granules. The 

 yolk is omitted from the lower part of the section in order to show the loose 

 protoplasmic mesh-work which pervades the embryo. 



Fig. 10. — A later stage in the development, showing several nodes of 

 various sizes, some with nuclei, some without. 



Fig. 11.— a stage in the development corresponding to that of Fig. 10, to 

 show the relation of the nuclei to the yolk. Each nucleus is situated in 

 a small protoplasmic area or node, and the yolk granules close to it are ex- 

 tremely small. 



Fig. 12. — The same stage as Fig. 10, showing the different phases in the 

 formation of the nuclei. The details of the yolk are omitted. 



VOL. VI. 8 



