PLATE X. 



1. Scopelus humboldti, showing luminous spots. 



2. Mother o'pearl organ from side of same. 



3. Argyropdecus. 



4. Longitudinal section of organs from abdominal region of same. 



5. Luminous organ from nasal region of Ichthyococcus. 



6. Luminous Crustacean. 7. Lampyris. 8. Light cells of same, and trachea (magnified). 



