PLATE VII 



FIG. i. Diagram of contiguous halves of an interambulacrum and an 

 ambulacrum of Plesiechinus ornatus^ showing " localized stages 

 in development." The first-formed plates (at the bottom 

 of the figure), and the last-formed plates (at the top) show 

 "youthful " characters of ornament. The full species-character 

 * s shown at the mid -zone. 





FIGS. 2-13. Morphogeny of some types of apical systems in the Echinoidea. 

 Fig. 2. Diademine (e.g. Hemipedina\ Fig. 3. Calycine 

 (Peltastes}. Fig. 4. Plesiechinus. Fig. 5. Pygaster. Fig. 6. 

 Holectypus. Fig. 7. Discoidea (the posterior genital is not 

 always perforated). Fig. 8. Clypeaster. Fig. 9. Anorthopygus. 

 Fig. 10. Spatangus (after Loven). Fig. n. Adult Spatangus 

 (after Loven). Fig. 12. Conulus. Fig. 13. Echinocorys. 

 For further explanation, see p. 94. 



