LIGHT PRODUCTION IN CEPHALOPODS. 159 



the luminous species, are (Egopsid. Among the QEgopsida 

 themselves over one half of all the families, genera, and species 

 are described as possessing photogenic organs. Five entire 

 families the Lycoteuthidee, Lampadioteuthidae, Enoploteu- 

 thidae, Histioteuthidae, and Benthoteuthidae, all of them of more 

 or less deep sea habit, have all their species so equipped, and 

 this seems almost certainly true of the very aberrant but num- 

 erous Cranchiidae as well. Among other groups of cephalopods, 

 only the Spirulidae can aspire to inclusion in the same category, 

 and regarding them our information is still deficient. There 

 may be only one valid species in this family. In addition to 

 those named, one other cegopsid family (Chiroteuthidae) has 

 more than half its species light producing. On the other hand 

 luminous species for five cegopsid families (the Architeuthidae, 

 Gonatidae, Thysanoteuthidae, Lepidoteuthidae and Grimalditeu- 

 thidee), five of the seven myopsid families, six of the eight 

 octopod families, and the Nautilidae, are as yet unknown. 



For multiplicity and variety of luminous forms the palm must 

 be awarded to the Enoploteuthidae and Cranchiidae, though, as 

 will subsequently appear, the maximum attainment and diversity 

 of structure of the photogenic organs themselves is reached not 

 in either of these families, but in the Lycoteuthidae. 



4. ACTUAL OBSERVANCE OF THE PHENOMENON. 

 As compared with other Mollusca, or even with other general 

 groups of Invertebrata, Cephalopoda, and especially those of 

 the decapod section, are extremely difficult either to capture, to 

 maintain alive under artificial conditions, or even to observe 

 with any degree of satisfaction in their free condition. Among 

 the (Egopsida it is probable that a sheer majority of the genera 

 have never been seen at all in the living state, at any rate by any 

 human eyes but those of fishermen. It is therefore not to be 

 wondered at that actual observance of the phenomenon of light 

 production in this group of animals is an extremely rare event, 

 possible only occasionally or under very exceptional conditions. 

 The published records of such observations are consequently so 

 scattered that they have fallen into obscurity, or else, in the 

 case of some of the more spectacular ones become all the more 



