494 PHYSIOLOGY. 



or quite bright colour ; it is strongest in the female, and shines uni- 

 formly, as in L. noctiluca and /,. splendidula, but in L. Italica and in 

 others * it varies in intensity in rhythmical vibrations ; during the 

 day it is not observed, and can be momentarily suppressed by night 

 at the will of the insect. This they appear to do in moments of 

 danger, at least I have often observed that those which I have caught with 

 my hat during flight immediately ceased shining, and so frequently 

 deceived me by my fancying that I had missed the creature, but I 

 afterwards discovered it in my hat, when it again shone. The light is 

 increased during motion as well as during exciting corporeal action, for 

 instance, during copulation and in great heat, but which must not be 

 much higher than 40 R. ; cold, however, speedily destroys the faculty, 

 and even at 10 beneath zero. If the insect be kept some days in the 

 dark it entirely loses its luminousness, but regans it upon being again 

 placed in the sunshine. After its death the light still lasts some hours 

 and even days, and even afterwards can be re-produced by warm water 

 or acids. All poisonous gases, which speedily kill the insect, destroy 

 just as quickly its light ; even in pure oxygen the light was indeed at 

 first brighter, but disappeared at the death of the insect. In heated 

 water, on the contrary, the light long continued in a temperature 

 not exceeding 50 R., but immediately disappeared upon the applica- 

 tion of greater heat, and also by degrees as the water cooled. Elec- 

 tricity has no influence upon the strength of the light, nor did it 

 produce any luminousness in insects already dead, whereas galvanic 

 electricity occasioned a much brighter light, and even re-produced the 

 luminousness in dead insects which no longer exhibited it. But these 

 effects are not produced in vacuum, nor if the creature be covered with 

 oil. Upon anatomical inspection there was found at the shining spots 

 a whitish, transparent, granulated mass, intersected by tracheae, and 

 which mass did not appear to be very different from the fatty substance. 

 This mass shines also for a time when removed from the body of the 

 insect, particularly in warm water, but it loses its light upon drying, 

 but regains it for a short time upon being remoistened. 



Among other beetles we find the Scarabeus phosphoreus named as 

 luminous, and upon which Luce has communicated some observations t. 



* See Gurus, at the above cited place, and in the Isis, 1824, vol. ii, p. 245, where it is 

 related, that according to Long, a New Holland species also exhibits this rhythmical 

 luminousness. 



t Roy.ier, Journ. de Phys. vol. xliv. p. .TOO. 



