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DESCRIPTION OF PLATES. 



All the figures were drawn with the camera lucida under Zeiss apochromatic 

 lenses, Obj. i6mm., Occ. 18. The positions of all the cell walls and nuclei were 

 represented with as great faithfulness as possible. With the exception of Figs. 

 69-73, PI. VI, which represent ova of Crepidula plana, all the preparations 

 figured are of C. fornicata. In Pis. II-VI the mesoblast is colored red, the 

 enteroblasts (intestinal cells) blue, mesentoblast violet. In PI. VII the violet 

 indicates the nervous system. In Pis. VIII and IX yellow indicates the yolk cells, 

 neutral tint ectoderm, and a darker shade of neutral tint mesoderm. 



