LIFE AND FORCE. 



between the male and female. PhosphoresceTioe is 

 probably much more common among insects than we 

 are at all aware of, as the behaviour of all sorts of 

 moths to the candle would suggest. Among the 

 most notable instances are the glow-worm and the 

 fire-flies, which are beetles ; and the Chinese lantern- 

 fly [Fulgora), related to the Italian grasshopper 

 {Cicada). Among the Crustacea there are also in- 

 stances of luminosity. Among the vertebrata, while 

 we find that luminosity is very common in fishes, 

 being exhibited always by some, and at seasons by 

 others, such as the common herring, yet it is doubtful 

 whether it occurs among the higher groups. 



In many of the more highly organized animals that 

 exhibit phosphorescence, the light, iustead of being 

 difi'used all over, is emitted by special organs. The 

 general type of these organs, in whatever part of the 

 body they are developed, seems to be that of a 

 glandular structure, secreting an oily fluid. The 

 phosphorescence is not attended with any heat be- 

 yond the natural temperature of any active gland, nor 

 does it seem to consume more oxygen than would be 

 accounted for by other active vital processes ; it is 

 therefore not connected with anything of the nature 

 of ordinary combustion. It has been attributed to 

 a slow oxidation of a fatty compound containing 

 phosphorus, phosphorus being, in minimal quantities, 

 a usual constituent of protoplasm, and an important 

 constituent of various animal fatty tissues. Phospho- 

 rescence sometimes continues after the death of the 



