4« 



ON LUMINOUS AKIMALS. 



existing at 

 particular sea- 



Two sacs in 

 the glovf- 

 worm. 



■which emit 

 )ight almost 

 constantly. 



Said to vary 

 in number. 



paler yellow colour. Tiiis substance does noit entirely cover 

 the innec surface of the rinjjs, being more or less deficient 

 along their edges, where it presents an irregular waving 

 outline. I have observed in the glow-worm, that it is ab- 

 sorbed, and its place supplied by common interstitial sub- 

 stance, after the season for giving light is past. 



The segments of the abdomen, behind which this pecu- 

 liar substance is situate, art thin and transparent, in order 

 to expose the internal illumination. 



The number of luminous^ngs varies in different species 

 of lampyris; and, as it would seem, at different periods in 

 the same individual. 



Beside the luminous substance ^bove described, I have 

 discovered in the common glow-worm, on the inner side of 

 the last abdominal ring, two bodies, which to the naked 

 eye appear more minute than the bead of the smallest pin. 

 They are lodged in two slight depressions, formed in the 

 shell of the ring, which is at these pwnts particularly 

 transparent. On examining these bodies under the micro- 

 scope, I found, that they were sacks, containing a soft yel- 

 low substance, of a more close and homogeneous texture, 

 than that which lines the inner surface of the rings. The 

 membrane forming the sacs appeared to l>e of two layers 

 each of which is composed of a transparent silvery fibre, 

 in the same manner as the internal membrane of respiratory 

 tubes of insects; except that in this case the fibre passes 

 in a spiral, instead of a circular direction. This mem- 

 brane, although so delicately constructed, is so elastic as 

 to preserve its form, after the sac is ruptured, and the con- 

 tents discharged. 



The light, that proceeds from these sacs, is less under 

 the control of the insect, than that of the luminous sub- 

 stance spread on the rings: it is rarely ever entirely extin- 

 guished in the season that the glow-worm gives light, even 

 during the day: and when all the other rings are dark, 

 these sacs often shine brightly. 



The circumstance of there being points, which give a 

 more permanent light than the other parts of the luminous 

 rings of the abdomen, has been noticed before by the 



Comte 



