1 86 S. STILLMAN BERRY. 



distal organs of the tentacles, the terminal members of the suboc- 

 ular series, and the gastric organs, all being of this category. 

 In the gastric organs, the respective masses of photogenic sub- 

 stance, though entirely distinct from one another, are contained 

 within the same capsule. In the case both of these and the 

 terminal subocular organs, which are separated, the accessory 

 photophore lies beneath the principal one and the rays which 

 emanate from it must accordingly pass through the latter if they 

 are to have egress at all. In Pterygioteuthis the branchial organs 

 are duplex, the accessory organ being contained a little to one 

 side of its principal, but still within the same pigment cup. 



8. POLYMORPHIC NATURE OF PHOTOGENIC ORGANS. 



The question is now very near, whether so many simple and 

 elaborate morphological types of light-producing organs have 

 any especially closer genetic relationship to one another where 

 they are found within one and the same species or genus. And 

 this leads easily to another, whether the photophores of any 

 given species exhibit such manifold structural diversity as to 

 render improbable their ultimate reduction to a single primor- 

 dial type. The affirmation of this latter question implies the 

 negation of the former, and I think we may certainly say that 

 this seems most truly to express the facts as we have them. The 

 accompanying table (Table VI.), which it has seemed worth 

 while to elaborate upon the basis of the interesting outline given 

 given by Chun, shows that whereas about a third of the genera 

 cited each possess photophores belonging to a single general 

 type, nearly as many have strongly dimorphic photophores, 

 and an even greater number have trimorphic or polymorphic 

 organs. It is nothing unusual therefore to find organs of extreme 

 simplicity functioning as components of the same photogenic 

 system which contains also organs exhibiting the most varying 

 degrees of complexity in structural plan. While this seems to 

 take place almost in hit or miss fashion, I think it may be taken as 

 a general statement of fact that those species having a relatively 

 abundant development of integumentary photophores distrib- 

 uted over the body generally fail to evolve a great variety of 

 other types, the Abralioid genera providing the nearest to an 



