LIGHT PRODUCTION IN CEPHALOPODS. 177 



ventral surface of the mantle only (Aneistrocheirus, Flyaloteuthis , 

 and, according to Chun, though he is controverted by other 

 writers, Chaunoteuthis) . In others (Eucleoteuthis] they occur on 

 the ventral surface of the head as well. In Calliteuthis, His- 

 tioteufhis and some species of Mastigoteuthis they are found not 

 only on the mantle and head, but on the aboral surfaces of the 

 ventral and ventro-lateral arms. In Mastigoteuthis agassizii 

 they are figured as occurring even on the tentacle stalks, as they 

 do likewise in Thelidioteuthis , although this would appear to be 

 an unusual situation for organs of the integumentary type. In 

 the former of these two genera they are numerous in the inte- 

 gument of the head, arms, and mantle as well as the tentacles; 

 in the latter, they are less numerous and although found along 

 the outer side of the tentacles, occur elsewhere only on the ven- 

 tral aspect of the mantle and head, where they have a very 

 regular and characteristic arrangement. Finally in a number of 

 well-known genera (Enoploteuthis, Abralia, Abraliopsis, Wat- 

 asenia, Mastigoteuthis}, integumentary organs are plentifully 

 distributed in indefinite number over the entire ventral aspect 

 of mantle, head, arms, and funnel. 



On the fins these organs appear less frequently, but they are 

 described as occurring dorsally in several species of Mastigo- 

 teuthis, and in one (M. talismani) on their ventral faces. 



In a number of species there is a particular development of 

 the integumentary photophores in the neighborhood of the eyes, 

 usually in the form of a circlet around the margin of the lid 

 opening, and such a circlet may occur, as in Enoploteuthis, 

 Abralia, Abraliopsis and Watasenia, in addition to a well de- 

 veloped series of subocular organs. As a general rule, and cer- 

 tainly in the four genera named, the organs comprising this 

 circlet are not to be distinguished from those of the general 

 integumentary surface save by their peculiar arrangement and 

 position. In the Histioteuthidse, however, comprising the genera 

 Histioteuthis and Calliteuthis, a most singular modification of 

 this feature is encountered. A peculiar attribute of these 

 genera is that, probably without exception, all the species have 

 the left eye enormously more developed than the right, so much 

 so in fact that a strong lateral torsion or displacement of the entire, 



