148 S. STILLMAN BERRY. 



On the other hand among the decapods photogenic properties 

 are so widespread that taking the class as a whole, and even 

 including the Octopoda, I am aware of no other major division 

 of metazoan animals which shows such a proportional develop- 

 ment of luminous species as the Cephalopoda. 



It is therefore no wonder that the scattered literature, as 

 well as the fragmentary character of the information to be 

 gleaned therefrom, offers almost insurmountable difficulties to 

 the inquiring student, while even reasonably complete informa- 

 tion is scarcely to be found in any text-book or work of reference. 

 There seems in fact no more recent effort on the part of teutho- 

 logists to meet this need than that of Chun (:io), which seems 

 to have been carried out simply as an incident to the preparation 

 of his monumental work on the "Valdivia" CEgopsids, an 

 expensive and in the United States a relatively inaccessible 

 volume. Furthermore he dealt with but one group of cephalo- 

 pods, while even for this group there has now accumulated a 

 considerable mass of additional information. In the English 

 language by all odds the best and most trustworthy summary 

 is the brief one of Hoyle (:o8). 



Probably the best way to convey an accurate idea of the man- 

 ner of distribution of the photogenic function within the group 

 is to present summarily a systematic survey of the entire class, 

 carried down at least as far as genera, and including at the same 

 time such appropriate supplementary data concerning the posses- 

 sion of this function as in each case is possible. An effort to do 

 this is constituted in the following synopsis. In all cases an 

 attempt is made to state as exactly as one writer can the number 

 of valid or recognized species in each genus, and, in the case of 

 photogenic forms, a full list of the species themselves, as well 

 as an indication of the situation of their photophores. In a 

 catalogue of this kind it must at the outset be admitted that 

 the figures given are only approximate, due to the fact that 

 entire elimination of the personal element is quite impossible, 

 even though the concrete numbers quoted are not mere estimates, 

 but represent in every instance an actual weighing of the validity 

 of each specific name in the light of all available information, 

 information which from the very nature of this paper cannot be 



