Davkni'okt — Cristatell;i. 



PLATE IV. 



All figures, except Fig. ;J9, are vertical riglit-aiul-left sections, and all are nKignified 



oOO diameters. 

 Figs. 24-20. Tliree sections from a series passing from the oral to the ahor/il face 

 of a polypide of about Stage X., and culling it in the jilanes indi- 

 cated by the lines 24-20, Fig. Vi. 

 " 27-29. Tliree sections of a series cut from a jjolypiile of Stage .\I. The 



planes of section are indicated in the lines 27-20, Fig 17. 

 ',' 30-32. Tlirt'e sections, whose j)ositions are indicated by the lines oU-32, Fig. 



18, cut from a polypide of Stage XII. 

 " 33-38. Six sections cut from a pclypide of Stage XIII. in the directions indi- 

 cated in Fig. 19 by the lines 33-38. 

 " 39. A horizontal section of a polypide somewhat older than that repre- 



sented in Fig. 18, and passing nearly in the direction of the line 43. 



