LIGHT PRODUCTION IN CEPHALOPODS. 169 



and allowed to rest quietly it may be taken into the dark-room 

 and gently struck, as it swims in the aquarium, with a glass rod. 

 Fig. 1 8 is a drawing to illustrate what may and usually does 

 happen under these circumstances. The animal throws out of 

 its siphon several little masses of mucus which show no light 

 at the moment of ejection, but almost instantly, as the oxygen of 

 the water begins to work on them, show a number of rod-shaped 

 particles of a brilliantly luminous matter embedded throughout 

 the very delicate mass. As the mass continues to expand this 

 light continues to glow brightly for as much as three to five 

 minutes, after which it rather suddenly dies out. In color the 

 light is the usual blue-green of luciferine when burning outside 

 the body. The animal can repeat this process for a number of 

 times, when it appears to have exhausted its supply of luciferine, 

 and it is not possible, apparently, to keep it in captivity for a long 

 enough period for the supply to be restored." 



From this scanty, but for all practical purposes probably ex- 

 haustive summary, we find that except for the doubtful obser- 

 vations by Souleyet, Darwin and Giglioli, the actual process of 

 light production in cephalopods has been observed directly in but 

 seven species, of which three belong to the myopsid family 

 Sepiolidse and have photogenic organs of a peculiar discharging 

 type, while the other four belong to the (Egopsida. We are 

 fortunate, however, in that each of these latter species is repre- 

 sentative of a different family and thus ample support is given 

 to the inferences necessarily drawn from the outward appearance 

 and histological structure of the many types of photophore that 

 they are of a fact photogenic. 



(To be Continued') 



