NATURAL HISTORY. 



641 



pressions, formed in the shell of 

 the ring, which is at these points 

 particularly transparent. On ex- 

 amining these bodies under the 

 microscope, I found that they were 

 sacs containing a soft yellow sub- 

 stance, of a more close and ho- 

 mogeneous texture than that which 

 lines the inner surfaceof the rings. 

 The membrane forming the sacs 

 appeared to be of two layers, each 

 of which is composed by a trans- 

 parent silvery fibre, in the same 

 manner as the internal mem- 

 brane of the respiratory tubes of 

 insects, except that in this case 

 the fibre passes in a spiral instead 

 of a circular direction. This 

 membrane, although so delicately 

 constructed, is so elastic as to pre- 

 serve its form after the sac is rup- 

 tured and the contents discharged. 



The light that proceeds from 

 these sacs is less under the control 

 of the insect than that of the lu- 

 minous substance spread on the 

 rings : it is rarely ever entirely 

 extinguished 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 therebeing 

 points which give a more perma- 

 nent light than the other parts of 

 the luminous rings of the abdo- 

 men, has been noticed before by 

 the Comte G. de Razoumouski. 

 He states the number of these lu- 

 minous points to vary from two to 

 five. 



I must however remark, that I 

 never saw more than two of these 

 luminous points, which were al- 

 ways upon the last ring of the 

 body, and that the figures which 

 accompany the memoir of the 

 Comte de Razoumouski, bear 

 Vol. LII. 



scarcely any resemblance to the 

 insect they are intended to repre- 

 sent ; from which we may fairly 

 suspect him of inaccuracy in other 

 particulars. 



As far as my observation has 

 extended, the small sacs of lumi- 

 nous substances are not found in 

 any species of lampyris, except 

 the glow-worm of this country. 

 Thunberg mentions that the lam- 

 pyris japonica has two vesicles on 

 the tail, which aflbrd light. 



The organs for the production 

 of light in the genus elater are 

 situated in the corcelet ; these 

 likewise consist of a peculiar yel- 

 low substance, placed behind 

 transparent parts of the shell, 

 which suffer the natural colour of 

 this substance to be seen through 

 them in the day, and when illu- 

 minated give passage to the light. 



On dissecting the organs of 

 light in the elater noctilucus, I 

 found that there is a soft yellow 

 substance, of anovalfigure,lodged 

 in the concavity of the yellow spots 

 of the corcelet, which parts are 

 particularly thin and transparerit 

 in this species. This substance is 

 so remarkably close in its struc- 

 ture, that at first view it appears 

 like an inorganic mass, but with 

 a lens it is readily perceived to be 

 composed of a great number of 

 very minute parts or lobules close- 

 ly pressed together. Around these 

 oval masses, the interstitial sub- 

 stance of the corcelet is arranged 

 in a radiated manner, and the por- 

 tion of the shell that immediately 

 covers the irradiated substance is 

 in a certain degree transparent, 

 but less so than that which lies 

 over the oval masses : it is there- 

 fore probable, that the interstitial 

 substance in this situation may be 



2 T 



