LIGHT PRODUCTION IN CEPHALOPODS. 1 67 



ventral surface of the mantle, head and siphon, and they are 

 also on the third and fourth arms. . . . 



"Each organ in the fresh specimen has a substance of purplish 

 hue in the centre; this substance seems to be that discharging 

 light when the animal is living. When the organ is exposed in 

 the air, the purplish hue of the substance changes to greenish 

 blue after a while, and finally resolves into a true green. The 

 substance is covered by a pigment layer of darkish brown or 

 deep purple which has a hole resembling the pupil of an eye, 

 through which the substance can easily be seen. The light of 

 the substance at night is whiter and less luminous than that of 

 the brachial organ. 



"Ocular Organ. When the eyelid of the fresh specimen is 

 removed and the eyeball exposed, there are seen 5 luminous 

 organs arranged in a series along the ventral circumference of 

 the eyeball, the organ on either end of the series being a little 

 larger than the remaining 3. The colour of all these organs 

 is pearly white. When the organ is seen at night in the living 

 animal, the phosphorescence is not distinguishable from that of 

 the minute organ on the body. 1 



"Difference of Phosphorescence in the Sexes. On examining 

 the preserved specimens to discover the difference of the external 

 forms as well as the histological structures of their luminous 

 organs as occurring in the male and female, none could be 

 discerned. But in the female specimens there are one hundred 

 or so more of the minute organs of the mantle than in the male. 

 Whether there is any meaning as to sexual selection, it is difficult 

 to say, the data concerned being insufficient at present to an- 

 nounce any opinion. 



"Next, as to the difference of phosphorescence between the 

 sexes in their living state, the means of investigation proved to 

 be very difficult. At first I repeatedly undertook to keep the 

 animal in an aquarium, but no success was attained. The 

 reason for the failure is that first of all, the animals are very 

 delicate, and next the aquarium was defective. The animals 



1 A slight discrepancy is noteworthy between the account of Sasaki and that of 

 Ishikawa concerning the character of the light of the subocular organs. According 

 to the latter these photophores are more or less intermediate in brilliancy between 

 the large brachial organs and those of the general integument. 



