INSECTS. 



^ra. The only animals wlilch appear to potTefs a diftinft 

 mganizatioii for the production of light are the foar ilrll 

 of tlic hift mentioned genera. 



" The light of the lampyrides (glow-worm) is known 

 to proeeed from fomc of the lail rings of the abdomen, which, 

 when not illuminated, are of a pale yellow colour. Upon 

 the internal furface of thcfe rings there, is fpread a layer 

 of a peculiar foft yellow fiibftance, which has been com- 

 pared to pafte, but by examination with a lens I found it 

 dfganizcd like the common interftitial A:bft:mce of the in- 

 fe^'s body, except that it is of a clofcr texture, and a 

 paler yellow colour. This fubftance does not entirely cover 

 the inner furface of the rings, being more or Icfs dciicient 

 along their edges, where it prefents an irregular waving 

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

 forbed, and its phice fupplied by common interftitial fnb- 

 ttance, after the feafon for giving light is pafl'ed. The 

 fegments of the abdomen, behind which this fabilance is 

 fituated, are thin and tranfparent, in order to expofe the 

 iuternal illumination. The number of luminous rings varies 

 in different fpecies of lampyris, and as it wo'jid leem at 

 different periods in the fame individual. Bolides the lu- 

 minous fubilance above defcribed, I have difcoyered in the 

 common glow-worm, on the inner fide of the laft abdominal 

 riiig, two bodies, which to the naked eye appear more 

 minute than the head of the fmal'dl pin. They are lodged 

 in two flight depreffions, formed in the fliell of tUe ring, 

 which is at thefe* points particularly tranfparent. On ex- 

 amining tliefe bodies under the microfcope, I found that 

 they were facs containing a foft yellow fubftance, of a 

 more clofe and homogeneous texture than that which lines 

 the inner furface of the rings. The membrane forming the 

 facs appeared to be of two layers, each of which is compofed 

 of a tranfparent filvery fibre, in the fame manner as the in- 

 ternal membrane of the refpiratory tubes of inferlls, except 

 that in this cafe the fibre pafies in a fpiral inllead of a 

 circular direction. This membrane, althougli fo delicately 

 conilru£led, is fo elaftic as to prcferve its form, after the 

 fac is ruptured, and the contents difchargcd. 



The light tliat proceeds from thefe facs is lefs under the 

 controul of the infeft, than that of the luminous fubft.ance 

 fpread upon the rings: it is rarely ever extinguiPned in the 

 feafon that the glow-worm gives light, even during the day ; 

 and when all the other rings are dark, thefe facs often fiiine 

 brightly. 



The organs for the produiflion of light in the genns 

 «latcr are fituated in tlie corfelet ; thefe likewife confill 

 of a peculiar yellow fubltance, placed behind tranfparent 

 parts of the (hell, which fuffer the natural colour of this 

 fubftance to be feen through them in the day, and when 

 illuminated give paifage to the hght. On difTcCting the or- 

 gans of light in the elater nodilucus, I found that there is 

 a Joft yellow fubftance of an oval firi'jre lodged in the con- 

 ; cavity of the yellow fpots of the corfelet, which parts are 

 particularly thin and tranfparent in tlus fpecies. This fub- 

 ' ilance is fo' remarkably clofe in its texture, that, at firft view, 

 it appears like an inorganic mafs, but with a lens it is rea- 

 dily perceived to be compofed of a great number of very 

 minute jiarts or lobules clofely preffed together. Around 

 thefe oval malles the interftitial fubftance of the corfelet is 

 arranged in a radiated manner, and the portion of the Ihell, 

 that irniiudiately covers the irradiated fubftance, is, in a cer- 

 tain degree, tranfparent, hut lefs fo than that which lies 

 over the oval maOes : it is therefore probable that the inter- 

 ftitial fubftance in this fitiialion may be endowed with the 

 property of Ihining. In the ekter iguitusthe mafles of In- 

 i nucous fubftance ire extreitu-ly irregular in their figure ; 



they are fituated nearly at tlie pollorior angles of the corfe- 

 let, and are more loofe in their texture than the oval niaftls 

 of the noftilucus, refembhng rather in compofition the in- 

 terftitial fubftance which furrounds thefe malfes in that 

 fpecies. The ftieil of the corfelet is foinewhat thinner, and 

 more tranfparent along both fides of the margin, than at 

 other places, but it is not, as in the nodilucus, elevated, 

 and peculiarly clear and thin immediately over the feat of 

 the luminous organ ; confequently the light emitted by the 

 elater ignitus cannot be very brilliant.'' 



In the fulgora candelaria and lanternaria, Mr. Macart- 

 ney has found the hollow organ, from which the light pro- 

 ceed;:, to commt;r.icate freely with the external air, by means 

 of a chink or narrow aperture, placed on each fide of the 

 root of the probofcis. This organ is lined by a membrane, 

 between which and the horny part or ftiell there appears to 

 be interpofed a pale rtddifh foft fubftance, arranged in lines 

 or ftripes in the candelaria. It could not be determinoJ, 

 whether this furnifhes the light, or is the pigment, upon 

 which the colour of the probofcis depends. 



The globes of the antenna: conftitute the organs of ligK 

 in the paufus fpherocerus. 



" It is worthy of remark," fays Mr. Macartney, " that 

 in all the difTeftions I have made of luminous infefts, I did 

 not find that the organs of light were better or differcnlly 

 fupplied with either nerves or air-tubes, than the other parts 

 of the body. The power of emitting light likewife exifts 

 in m:\ny creatures, which want nerves, a circumftance flrongly 

 marking the difference between animal light and animal elec- 

 tricity." Swammerdan's Book of Nature, or Hiftory of In- 

 fects : Lyonet Traitc Anatomique de la Chenille, qui rouge 

 le bois de faule : Cuvier Legons d'Anatomie comparee. 



In.sects infejlmg ike human body. The parafilic animals, 

 which are moll commonly found inhabiting, and deriving 

 their nutriment from, the internal cavities of the human 

 body, are the three fpecies of worms, which are denomi- 

 mated, by naturalifts, nfcaris, lumbrkus, and tsnia ; that is, 

 the maw-worm, or thiead-worm, round-worm, and taoe- 

 worm ; ts which may be added the tr'ichur'ss, wliich is 

 occafionally feen. (See thefe words. ) The external parts 

 of the body, again, afford a nidus and fuftenancc to one 

 or two of the infect tribes, cfpecially the pedicuU of the 

 head and of the piihcs ; the former of which are fonietimes 

 bred in great numbers, and infcft other parts of the furface, 

 producing a loathfonie and very obftinate difcafe, the mor- 

 bus p:Jicufaris, or luufy difeaie. (See Phtuhuasis and 

 Pitt'RiGO.) It is not our objeft, however, to treat of thefe 

 under the prefent article ; but merely to notice briefly the 

 occafional exiftence of various fpecies of the -zvinged in- 

 fccis, in the different cavities of the human body, efpecially 

 in I heir firft: ft;ate, that of larva, caterpillar, or grub ; and 

 to point out the manner in which they are probably intro- 

 duced. 



The medical writers of the fixteenth and early part of the 

 feventeenth century have recorded inftances of,v.irious reptiles 

 and otheif animals, which were difiodged front their abode 

 in different parts of the body, fiich as frogs, lizards, fer« 

 pents, &c. ; which may be found on confulting the collec* 

 tions of Bonlli, Marcellus Donatus, Schenck, and others. 

 But their credulity was at leaft equal to their learning and 

 induftry, and fublequent obfervation has not confirmed their 

 ftatenients, which probably originated from g^rofs ignorance 

 of the economy of thefe ci-eatuics, or from wilful decep- 

 tion on the part of thofe from whom they were faid to have 

 been dilcharged. On the other hand, the microfcopic 

 philofopher.s not only peopled every organ of the body \A>ith 

 woniii and nniiiialculcj ; but bei.cved that all contagion 

 A a 2 confilkd 



