LIGHT PRODUCTION IN CEPHALOPODS, II

AN INTRODUCTORY SURVEY

¹ REDLANDS, CALIFORNIA

1. Light production is an unusually widespread phenomenon in the molluscan Class Cephalopoda.

2. Although unknown in the Order Tetrabranchiata, scarcely developed in the octopod section of the Dibranchiata, and occurring little more than sporadically among the Myopsida, over one half of all described gopsida are known to possess photogenic properties.

3. The actual production of light by living cephalopods has been observed only rarely, but in species of sufficiently diverse relationship to confirm the evidence drawn from the morphology and histology of organs found in the remaining species.

4. The light of some species exhibits remarkable brilliance.

5. The color of the light emanating from the respective organs within the same species or in different species may exhibit striking differences in both intensity and quality, but it is not known to what extent this is actually due to inherent diversity in the physical properties of the light rays themselves.

6. Photogenic organs may occur in almost any portion of the body in this group of animals, but the outer integument, eyeball and pallial chamber are the situations most favored. They are often internal and able to function only by reason of the transparency of the body tissues in the living state.

7. The organs are predominantly, but by no means exclusively, ventral in distribution.

8. The organs are strongly polymorphic, even in the same species, varying from comparatively simple bodies of photogenic tissue to the highly complex "searchlight" types.

9. Numerous duplex organs, or organs with accessory photophores, are known to occur.

10. Luminous organs in the Myopsida are usually of the type known as discharging. Those of the other groups are entirely of the enclosed or ductless type.

11. The maximum polymorphism in the photophores of any single species occurs in Nematolampas regalis Berry, from the Kermadec Islands, where the 90 or more organs are elaborated upon 12 or 13 more or less diverse structural principles.

12. The occurrence, distribution, arrangement, and morphological detail of photogenic organs in cephalopods are features of considerable taxonomic importance and yield valuable clues as to the relationship and classification of the genera and species even where still unknown anatomically.

13. The best evidence seems to indicate that the photogenic organs in this group of animals are polyphyletic and more or less sporadic in origin, hence that light production in cephalopods is not an essentially primitive or ancestral function to be regarded as now lost in many members of the group.