LIGHT PRODUCTION IN CEPHALOPODS. 189 



The photogenic systems of all the species of the eight genera 

 having polymorphic organs are outlined in further detail in 

 Table VII. Those species considered having the mere largest 

 number of photophores are the three Abralioids, occupying the 

 three central columns of the table, but those exhibiting the 

 highest degree of polymorphism are Lampadioteuthis megaleia, 

 which has not been investigated histologically but must have not 

 less than seven or eight types of photophores in all, Lycoteuthis 

 diadema, with ten types, or thirteen, if the accessory organs are 

 counted in, and Nematolampas regalis. Lycoteuthis diadema, 

 with the immeasurable advantage of having had its marvelous 

 photogenic properties observed in the living state, is usually 

 cited as the example par excellence of a luminous cephalopod. 

 However, it is evident from sheer morphological grounds that 

 even this wonderful creature must yield the palm to another, if 

 nearly related, genus and species, the truly amazing Nemato- 

 lampas regalis of the Kermadec Islands. Whether this species 

 will ultimately be found to display all the varied brilliance of 

 the red, white, and blue lights of Lycoteuthis, the fact remains that 

 in addition to a complete series of exactly homologous organs, 

 it has an entire battery of pyrotechnic engines of its own, so 

 there is every reason to expect a more rather than a less elaborate 

 illumination. The total number of photophores in this species 

 is in excess of ninety, which are elaborated upon no less than 

 twelve or thirteen different structural principles of uncertain 

 homologies with one another. Counting in the three types 

 of accessory photophores which are to be found in the eight 

 "double" organs (proximal tentacular, terminal subocular, and 

 anal), the total number of types is increased to fifteen or sixteen. 

 Which of the alternative figures quoted is the correct one is still 

 to be established by histological work. 



9. SYSTEMATIC SIGNIFICANCE OF PHOTOGENIC ORGANS. 



It follows almost as a corollary from what has been said in the 

 foregoing sections of this paper that the photogenic system 

 evinces a complex of features of the utmost value to the taxono- 

 mist. Of late years ever increasing weight has been given to it, 

 and the presence of constant differences, even though minute, in 



