158 



S. STILLMAN BERRY. 



TABLE III. 



SUMMARY. 



of 7 families, 29 genera, and 33 species. Chun (:io, p. 39), 

 treating only of the CEgopsida, increases these figures to 8 

 families, 26 genera and 39 species. The two sets of figures 

 should be compared with those given in the numerical summary 

 in Table III at the top of this page. Here it appears that of 

 the 32 families of recent cephalopods now recognized, 14 (or 

 more than two fifths) contain luminous species; out of 119 

 genera, 47 (or nearly two fifths) are light producing; and out of 

 595 species, 128 (or over one fifth) are now held on good ground 

 to be luminous. The rich development in species of the genera 

 Loligo, Sepia and Polypus, which has already been noted, is the 

 circumstance chiefly responsible for the cutting down of the 

 proportion which the luminous species bear to the whole to less 

 than one half that which is exhibited by the luminous families. 

 Similarly the slight proportional decline in the case of the lumi- 

 nous genera is due to the large number of ranking genera in 

 certain mainly non-luminous families such as the Ommastre- 

 phidae, Sepiolidae, Cirroteuthidae and Polypodidae. 



The table also indicates very strikingly what is really the 

 outstanding feature of the taxonomic distribution of the photo- 

 genic forms, namely, the preponderance both of CEgopsida among 

 the species known to be light producing, and of light producing 

 species among the CEgopsida. In the former instance this 

 preponderance is enormous. 71.4 per cent, of the luminous 

 families, 83.0 per cent, of the luminous genera, 77.3 per cent, of 



