26o 



THE AMERICAN ENTOMOLOGIST. 



from a lower or Fhyliocnistis-\\kt form. 



The first form of trophi seems to be 

 correlated with membraneous legs. At 

 least in every instance where the first form 

 is found, the legs are membraneous and 

 retractile. And when the trophi are 

 changed, and the second or ordinary form 

 assumed, usually at the same molt, the 

 thoracic legs become jointed and armed 

 with a claw, and the ventral legs are armed 

 with the circle of tentacles. But these 

 rules are not universal, for Phyllocnistis and 

 Lithocolletis of the flat group never acquire 

 the jointed legs, claw or tentacles, even 

 when they acquire the second form of tro- 

 phi. So, too, there are many larvse of other 

 genera, which, if they ever have trophi of 

 the first form, must possess them whilst in 

 the egg, for they leave it with trophi of the 

 second form ; and though usually (in all (?) 

 macro and most micro) lepidoptera, jointed 

 legs, with claw and tentacles are associated 

 with the second form of trophi, yet there 

 are many genera of Micro-lepidoptera 

 which, with the second form of trophi, are 

 either apodal or have membraneous legs 

 without claw or tentacles. Thus, Aspidisca 

 has sucker-like discs in place of the thoracic 

 legs, and no ventral legs ; Antispila is apodal ; 

 Nepticula has a surplus number of mem- 

 braneous legs ; while all of them have tro- 

 phi of the second form from the time they 

 are hatched. Tischeria, some Gelechia, and 

 some other leaf -mining larvae, on the other 

 hand, leave the egg fully developed cater- 

 pillars, with trophi of the second form 

 (Fig. 124), articulated thoracic legs armed 

 with a claw, and ventral legs armed with a 

 circlet of tentacles. 



All of the genera above mentioned have 

 leaf-mining larvae.* Usually, soon after the 

 articulated legs are developed, they leave 

 the mine and either feed or pupate exter- 

 nally. The change is usually preparatory 

 to leaving the mine. But some of them, 

 as the flat and cylindrical groups of 

 Lithocolletis, some species of Gracilaria do 

 not leave the mine even after the change ; 

 though most Gracilaria, even when they 



* This is only true as to Gelechia in part ; the greater nur 

 ber of Gelechia larvae are not leaf-miners. 



continue to be leaf-miners, leave one mine 

 and make another. Some, however, as 

 Gracilaria erigeronella Cham., and all Lith- 

 ocolletis of the flat and cylindrical group, 

 never leave the mine at all. On the other 

 hand, Nepticula, with its membraneous feet, 

 Antispila, footless, and Aspidisca,yN\\}!\ suck- 

 ers in place of feet, leave their mines to pu- 

 pate, and Nepticula has even been known to 

 leave one mine to form another. Phylloc- 

 nistis never leaves the mine until the imago. 



Can it then be said that these various 

 structures are the result of conditions of 

 existence or adaptability ? All are leaf- 

 miners, subject, as their ancestors have 

 been for ages, to the same conditions of 

 life within the mines. Usually, preparatory 

 to leaving the mine, and before leaving it, 

 a change takes place which fits them for 

 different conditions and a different mode 

 of life ; but, as above stated, many even 

 then remain in the same conditions. In 

 many of them {Phyllocnistis and the flat 

 group of Lithocolletis e. g.) the articulated 

 legs are not acquired until the insect passes 

 into the pupa state, which is wholly one of 

 preparation, and in which apparently they 

 have no use for any legs ; and these same 

 species, though they acquire the second 

 form of trophi, have no use for any of its 

 organs except the spinneret ; others, after 

 acquiring the second form of trophi, use 

 them for feeding in the mine, while a still 

 greater number use them for feeding out- 

 side of the mine. What figure does the 

 theory of the origin of organs, by adapt- 

 ability to conditions of existence, cut in all 

 this jumble ? 



How shall we account for these facts by 

 any theory of evolution ? There is of 

 course a clear process of evolution in the 

 history of each individual. There is 

 the first form of trophi with membrane- 

 ous legs ; then follow the second form of 

 trophi, usually accompanied by articu- 

 lated legs ; then follow the trophi of 

 the pupa and imago, always with artic- 

 ulated legs. Then, in another set of 

 larvae we never find the first form, but 

 we find the second form of trophi when 

 the larva leaves the egg, and usually 



