472 E. M. PACE. 



26. Wallace, W. — "OLi&ervalioiib on Ovaiiau Ova and rolJicles in Certain 



Teleostean and Elasniobrancli Tishes," ' Quart. Journ. Micr. Sci.,' 

 n.s., vol. 47, pp. 161-213, pis. 15-17, 1903. 



27. Wilson, E. B. — " On Protoplasmic Structure in the Eggs of Ecliinoderms 



and Other Animals," 'Journ. Morphol.,' vol. xv, suppl., pp. 1-25, 

 pis. i, ii, December, 1899. 



Postscript. — Since the above account of the yolk nucleus 

 in the egg of Flustrella hispida was written, a paper (24) 

 has appeared by O. van der Stricht on the yolk nucleus in the 

 eggs of miimmals. The account of the yolk nucleus given by 

 this author appears in the main to confirm Bambeke^s observa- 

 tions and views. 



EXPLANATION OF PLATES 22—25, 



Illustrating Mrs. R. M. Pace's paper on "The Early Stages 

 in the Development of Flustrella hispida (Fabricius) ." 



Reference Letters.- 



J. Aboral surface of larva. A.Ec. Aboral ectoderm. Bl. Blastopore. 

 C. Ciliated crown, corona, or " couronue." Ca. Aboral organ or " calotte." 

 Ci. "Eenle ciliee." cr. Crystalloid bodies. C.T. "Papille dc plumet vibratile,'' 

 ciliated tuft. Ee. Ectoderm. Ed. Endoderm, or mesendoderni. Fo. Follicle 

 cells. Fs. "Possette supcrieure." Fu. Puuicle. G. Chromatin granules. 

 ff. Globules in cells of pharynx and internal sac. /. Intestine. I.S. Internal 

 sac. M. Muscle fibres. M.C. Aboral groove or mantle cavity. 3fc. Mesen- 

 chyme lining of zocecium. N. Nucleus, u. Nucleolus. NJJ. Neuro- 

 muscular cord. 0. Oral surface of larva. Oe. (Esophagus. O.Ec. Oral 

 ectoderm. 01. Oil globules. Ov. Ovary. P.B. Polar bodies. P/i. Pharynx. 

 Fy. Pyriform organ. E. Rectum. S. Shell. S.C. Segmentation cavity. 

 S.G.' "Systcme glaudulaire supcrieure." S.G." "Systemc glandulaire in. 

 fcrieure." SL Stomach. T. Testes. I'.S. Tentacle siicath. vc. Vacuoles 

 iu the yolk nucleus. F.M. Vitelline membrane, x. Space or clear zone 

 surrounding the yolk nucleus. F. Yolk spherules. F.N. Yolk nucleus. 

 Z. Zocecial cavity. Those tissue tracts vphich are possibly to be regarded as 

 being destined to give rise to the mesoderm are marked by a small asterisk. 



