NOTES ON THE LIFE-HISTORY OF NEPTICULA ACETOS.'E, STT. 251 



inactive larva without locomotive organs, for the thoracic pads do not 

 seem capable of progressive action when the larva is out of the mine. 

 There are no visible seta?, and the only movements the body seems 

 capable of, are lateral, the head and thorax can be moved from side 

 to side, at least in the third instar. In the fourth (and last) instar, 

 however, instead of the helpless larva, we find quite an active little 

 caterpillar, provided with its due quota of setje and a number of leg- 

 like organs, by which it can make fairly rapid progress, and, besides 

 this, it is endowed with a set of muscles which enables it to accomplish 

 at least one gymnastic feat. This great difference between the third 

 and fourth instars probably accounts for the longer period of time 

 occupied during the third ecdysis, which, in some cases, lasted over 24 

 hours, and though I have no precise note on this point, I think the 

 period is generally longer. Owing to the very thick cell walls of 

 the sorrel leaf it is difficult, if not impossible, to observe the larva 

 changing its skin, but I imagine it is like other Nepticulids in this 

 respect and pushes the old head aside, then continues feeding till it is 

 out of the old skin. On three occasions when I took larvae in the 

 fourth instar out of the mines, I found the head of the third instar 

 adhering to the 8th or 9th abdominal segment. The larvae, probably, 

 in their progress, had brushed the old head along with them. By the 

 way, by the above remarks I do not mean to say that the larva, even 

 after having assumed the fourth instar some hours, is capable of the 

 activity I mention, for this is gradually developed as the larva comes 

 to maturity. Having entered on the fourth stadium, the larva usually 

 mines one circle round its home before, as Stainton says, " it flies off 

 at a tangent into an irregular tortuous gallery" {In><. Brit. Tin., p. 303). 

 The gallery is now greenish, or sometimes pinkish-white, about Imm. 

 in width, with a rather thick, irregular, and often interrupted, line of 

 dark excrement, sometimes running down the centre and sometimes 

 down the side of the gallery. The course of this part of the mine 

 is somew-hat dependent on the leaf in which it is situated. If there be 

 ample space, the larva will make two or three rather sharp turns in 

 the leaf, above the earlier part of the mine, that is, towards the apex 

 of the leaf, and then one bold sweep before the end. If, on the con- 

 trary, the leaf be very narrow or much occupied by other mines of X. 

 acetomi', the larva has to feed where it can find a vacant space, and the 

 mine in consequence becomes very irregular. In one much eaten 

 leaf, now before me, the larva has made two turns above the red part 

 of the mine and then gone as closely as possible along the margin of 

 the leaf, right round the apex to the opposite side, without making 

 any deviation at all. More often the larva has to work its w^ay with 

 many turnings in order to avoid those parts of the leaf already eaten 

 or occupied by its companions in the same leaf. I may say here that 

 the larvse seem to be of a remarkably gentle disposition, as in crowded 

 leaves I have noticed them running side by side for some distance, in 

 practically the same mine, without showing any signs of hostility, 

 just as we sometimes see the larvae of ('hrysopora heriuoiniella mining in 

 couples in the leaves of t'liennpodium. I have never attempted to 

 ascertain the sexes of individuals thus running in double harness. To 

 return to that portion of the mine made after the larva breaks away 

 from the blotch-like part, though fairly even in width it is variable in 

 length, depending possibly mainly on the nourishment afforded by the 



