December 9, 1915] 



NATURE 



413 



'lash, yellower than that of P. sciutillans; the female 

 replies with a double flash, the first sharper and 

 brighter than the second, followed at once by the 

 second. The reply is given very quickly after the 

 flash of the male. 



P. castus. — The male gives a single flash, not so 

 -hort and sudden as that of P. marginellus ; the female 

 :^ives a single flash very much like that of P. scin- 

 tllans, but delivered immediately after the flash of the 

 uale; there is no distinct pause as in P. pyralis, and 

 .0 indication of doubling as in P. marginellus. 



P. castus and P. viargiin'Uus are very similar, and, 

 indeed, by some authorities, have been considered to be 

 :nerely forms of one species. Mr. McDermott admits 

 hat he can find no points of structural difi^erence 

 oetween them, but considers them distinct species on 

 iccount of the very different flashes emitted by them, 

 rhey are frequently found flying together, but no case 

 if interbreeding has been observed, though especially 

 satched for. 



Mr. E. E. Green ' has published notes on the use of 

 I he light by certain species of luminous beetles in 

 Ceylon. Of these, one, Lainprophorus tenebrosus, 

 Walk., belongs to the Lampyridae properly so called. 

 The female of this species is apterous with a ventral 

 >ubterminal light-organ which she exposes much in 

 the manner of our glow-worm. The male, though 

 normally brilliant, approaches a "calling" female with 

 the light shut off, its advent being heralded only by 

 lie partial extinction of the light of the female. 



The other species mentioned by Mr. Green present 



'•rtain marked differences from normal Lampyridae 



in the emission of their light as well as in structural 



points, and have been placed in a separate family, 



Rhagophthalmidae. Concerning the light of Dioptoma 



iuiamsi, Pasc, Mr. Green notes the larviform female 



was observed to recurve the body over the back so as 



:.^ expose the ventral subterminal light organ. On the 



pproach of the male the light was partially -eclipsed 



ind the tail turned down. The male at the time was 



:ot known to be luminous, but under the stimulus 



f sexual excitement. It was observed to exhibit a 



v)w of luminous spots along each side of the abdomen, 



is well as dorsal spots on the abdomen and across the 



jase of the thorax. 



I have recently received from Mr. Gairdner, of 

 Bangkok, some females of a glow-worm which, he 

 reports, turn up their tails to exhibit the light in a 

 similar way to Dioptoma. Like the female Dioptoma, 

 too, they are of a more degenerative type than 

 Lampyris females, the antennae and legs being small 

 and feeble with a reduced number of joints. 



Allied to these and to the Lampyridae is another 

 Miiall family, the Phcngodidae, many of the members 

 f which TX)ssess very remarkable luminous proper- 

 ties. In Brazil and .\rgentina, for example, is an 

 insect that on account of Its peculiar scheme of 

 luminositv has long been known as a " railway " 

 larva. The head of this creature jjlows brightly with 

 a red light, like a live coal, which is more or less 

 intermittent in character, while along each side of the 

 body is a row of more constant lights, green or 

 vellow, or even changing at intervals from a bluish to 

 a more yellow hue. For manv years these "railway" 

 larvae were nothing more than a puzzle to ento- 

 mologists. On account of their Ught-givlne powers 

 they were usuallv considered to be lampyrid larvae, 

 though nothing else like them was known' Still les.s 

 were they like the larvae of the only other known 

 luminous coleopterus family, the Elateridae. The 

 astonishment was great when in 1885* it was an- 

 nounced that the botanist, Hieronymus, had found 



' Trans Ent. '^oc., loit.p. 717. 



* Haa«e, Sitzune. Natur. C,e». fsh., p. 10 • and Deutsche Enl. Zeil., 

 xxxii., p. 1C4 ; "Cam*^. Nat. Hi>t. In« ." pad ii., p. 231. 



NO. 2406, VOL. 96] 



one of these so-called "larvae" mated with a beetle 

 belonging to the genus Phengodes. Eggs were ob- 

 tained from it which in due course produced larvae, 

 thui proving that the supposed larva was in reality 

 the sexually mature, though degenerate and com- 

 pletely larviform, female of a beetle. 



We are now confronted with the very interesting 

 question as to whether the apterous, more or less 

 larviform, state of the females of many of these glow- 

 worms is a primitive condition or the result of de- 

 generation from an earlier, higher, winged type. Riley " 

 states that the female larva of Phengodes laticollis 

 and Zarhipis riversii, both North American species, 

 goes through a pseudo-pupal state prior to the final 

 moult. It appears, therefore, that this larviform 

 female is a mature though degenerate female, and that 

 we have not here to do with a case of paedogenesis ; 

 i.e. of the larva becoming sexually mature without the 

 attainment of somatic and metamorphic maturity. 



The same writer considered that we here "get a 

 glimpse, so to speak, into the remote post, from 

 which has been handed down to us, with but little 

 alteration, an archetypal Hexapod form which pre- 

 vailed before complete metamorphosis had origin- 

 ated." Were this really the case, it is difficult to 

 account for the occurrence of a pupal state in the 

 individual development of the female, though this 

 might perhaps be interprtted as a partial transference 

 from the metamorphosis of the male. Further, if the 

 larviform condition is to be explained as a case of 

 arrested development and the persistence of a primi- 

 tive type, either one would expect to find it fairly 

 constant in a group of closely related species, and 

 genera evidently arising from a common ancestry, or 

 It must be considered as a kind of throw-back or 

 reversion to an ancestral type. 



For mv part I prefer to regard the theory of de- 

 gradation from an earlier winged type as affording 

 a better explanation of the facts as we find them. 

 We have the successive stages in such degeneration 

 all illustrated, from the fully winged though sluggish 

 female of Luclola, through the brachypterous state 

 found in the females of certain species of Photinus, 

 down through the apterous but otherwise develop- 

 mentallv mature females of Lampyris, and the more 

 degenerate type of female of Dioptoma to the com- 

 pletely larviform females of Phengodes. The steps 

 in this series do not imply relationship or common 

 ancestry, but merely indicate the points, successively 

 further and further back in the phylogeny of the 

 group, when the use of the wings In the course of 

 any particular line of development was discarded and 

 their consequent degeneration set in, or, to put it 

 brieflv, that the apterous condition is of polyphyletic 

 origin. I know of no instance amontr the Lampyridae, 

 such as we have amongst the Lepldoptera with ap- 

 terous females (e.g. Anisopteryx aescularia) where, 

 though wings are wanting in the adult, there are well- 

 dev(jloped wing rudiments In the pupa, but I have 

 found one female of Lampyris noctihica with the 

 wing and wing-cover well developed, though shrivelled, 

 on one side of the bodv. 



With the question of the evolution of the apterous 

 female is bound up the question of the evolution of 

 the power of luminosity. Many members of the 

 family Lampvridae are probably not luminous at all. 

 Pale yellowish abdominal spots are almost always to 

 be detected in the region of the luminous organ, but 

 whether the species possessing them are always 

 luminous is open to doubt. Our knowledge of the 

 habits of manv of these insects =s extremely defective, 

 and it is frequently impossible •■> say from dried 

 specimens whether a species is or is not luminous. 



8 £m/. Afp. Afn/;., xy'iv., ^SS^, p. 148. 



