192 S. STILLMAN BERRY. 



nishes some delving student just a little better base of attack on 

 his problem than might otherwise have been afforded him, its 

 purpose will have been fulfilled. 



12. SUMMARY. 



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 occur- 

 ring little more than sporadically among the Myopsida, over one 

 half of all described (Egopsida 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 physi- 

 cal 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 trans- 

 parency 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 photo- 

 phores, 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 



