Plate XVI. 



Fig. I. Interambulacral area of Stereocidaris ingolfiatia. ^U. 



2. — — - Echinus acutus^ \'ar. Fleimngii. '/i. 



— 3. Apical area of Echinus elegans. ^/j. 



4. — — - Strongylocentrotiis drebachiensis. ^/i. 



c — — - Echi7t?is acuhis^ var. norvegiciis. 



'U- 



_ 6. — - — a/finis. Vi- With two pores in one of the genital plates. 



7. — — - — esculenttis. ^/i- 



_ 8. — — - — Alexandri. ^/i. With two pores in two of the genital plates. 



n. — — - Strongylocentrotiis drebachiensis. ^/i. 



10. — — - Echinus acuiiis, var. Fleiningii. ^/t. 



II. Interambulacral area of Strongylocentrotiis dr0bachieusis, f. granularis. ^/,. 



— 12. Plates from the buccal membrane and the gills of Echinus esculenttis. a. b. from the buccal 



membrane outside the buccal plates, c. from inside the buccal plates, d. e. f. from the 

 gills. Obj. II. Oc. III. 



— 13. Plates from the buccal membrane of Strongylocentrotiis drobachiensis. a. outside, b. inside the 



buccal plates. Obj. II. Oc. III. 



— 14. Plate from the buccal membrane of Parechiniis microtuberciilatns. Obj. II. Oc. III. 

 15. - — — -_ - _ miliaris. Obj. II. Oc. III. 



— 16. Plates from the buccal membrane and the gills of Echinus acutns, var. Flemingii. a. b. from 



the buccal membrane outside the buccal plates, c. from inside the buccal plates, d. e. f. from 

 the gills, a. b. Obj. II. Oc. I., c— f. Obj. II. Oc. III. 



— 17. Interambulacral area of Strongyloce^itrotiis drobachiciisis, i. pallidus. Vi- 



— 18. Ambulacral area of Echinus aciitiis^ var. Flemingii. 7i- 



— ig. — — - — elegans. ^/i. 



— 20. — — . — afftJiis. Vi- 



— 21. — — - Strongylocentrotus drebachietisis.! f. granularis. ^/i. 



22. — — - Echinus acutus., var. norvegicus. 



2/ 



/!• 



23. — — - Strongylocentrotiis drebachiensis^ f. pallidus. 



2/ 



