176 S. STILLMAN BERRY. 



these photophores are covered by the double fold of the integument 

 which forms the eyelid, and consequently in preserved specimens 

 are often invisible without partial dissection. But in the Cran- 

 chiidse the overlying membranes are thin, transparent, and very 

 insufficiently equipped with chromatophores, so that in good 

 specimens the organs may be clearly seen from the exterior. 

 And likewise in certain other groups such as Enoploteuihis and 

 the Abralioid genera, we find a delicate, transparent, elongate- 

 oval "window" in the integument, nearly or entirely free of 

 pigmented chromatophores, and overlying that portion of the 

 eyeball where are borne the photogenic organs. There can be 

 little doubt that this functions in aid of the latter by facilitating 

 the passage of their rays. 



The next most frequent topographic type of photophore to be 

 met with comprises those occurring in the general integument of 

 the body, primarily on the mantle, head, and arms. A remark- 

 able peculiarity of the integumentary organs is that they, like 

 the subocular photophores, are generally confined to the ventral 

 aspect and this circumstance has given rise to some interesting 

 theories regarding the origin and ecologic significance of the 

 whole phenomenon of light production in this group of animals. 

 Some writers have gone so far as to state that the distribution of 

 these organs is entirely ventral, but this is not in strict accord 

 with the facts, there being a few scattered photophores on the 

 dorsal aspect of the mantle in such forms as Abralia astrolineata 

 and most of the Histioteuthidse, while Verrill's figures show them 

 to be quite as strongly developed in this region in his Masti- 

 goteuthis agassizii u as they are below. Certain other species of 

 Mastigoteuthis have them in plenty on the dorsal surfaces of 

 the fins, even if not upon the body proper. Again in Professor 

 Joubin's anomalous Melanoteuthis the supposed photophores 

 are entirely dorsal. The possibly photogenic tubercles of Masti- 

 goteuthis cordiformis should likewise be recalled in this connection, 

 and finally the presence of photophores on the dorsal arms of 

 Nematolampas and Benthoteuthis. But even as many exceptions 

 as this serve principally to accentuate the prevalence of the rule. 

 In some genera the integumentary organs are developed on the 



Bull. Mus. Comp. Zoo/., V. 8, PI. I., 1881. 



