i8o 



BIOLOGICAL LECTURES. 



type of luminous organ, in which photogenic substance never 

 leaves the body, is illustrated by the more familiar phosphor- 

 escent organisms, such as fireflies (Fig. i), glowworms, Pyro- 

 pJioriis, EupJimisia, NyctipJianes (Fig. 2), PJiengodes, Scopehis 

 (Fig. 3), etc.i 



The phosphorescent organism of this group, as a rule, has 

 good control over its luminous organ, and may often be able to 



Fig. I. — P/wii>ms C0fzsang7ii?ie!is, right fig\irt,/ejnale ; Icil, iizaie. Luminous 



organs are shaded. 



inhibit the exhibition of light for a considerable length of time. 

 The organism may be endowed with a wealth of structures sug- 

 gestively like the luminous organs, yet they may never satisfy 

 the naturalist that they are such. if the exhibition of their lumi- 



1 It is impossible to give any adequate idea of the beauty and complexity of 

 the luminous mechanism of this type without the use of a large number of illus- 

 trations. Some ideas in regard to the size and distribution of the luminous organs 

 that obtain in some forms may be gathered from a few figures that accompany the 

 present paper. 



