LEPIDOPTERA OF NEW YORK 'AND NEIGHBORING STATES 163 



Mo and M ;! , Cu., and either M. s or Cu 1 apparently always preserved. 

 The free tip of H l is preserved in primitive forms, apparently arising 

 from the cross vein connecting Sc and R. Anal region obsolete. 



The caterpillars (figs. 121, 122) always leaf (or bast) miners, at 

 least when young, often changing their habits when part grown and 

 forming nests in a folded leaf. Young caterpillar unique, specialized 

 for feeding on the sap of the cells, which it opens with its blade-like 

 mandibles ; much flattened ; lobed at the sides ; widest near the anterior 

 end. Head extremely flat; front widening toward the posterior end; 

 adfrontals not normally recognizable, perhaps obsolete; maxillag and 

 labium very narrow as a rule, strap-shaped, and almost wholly incorpo- 

 rated in the head capsule, the free part of the maxillae and labium 

 minute. Ocelli reduced in size or number (frequently to a single pair). 

 True legs sometimes absent ; body-setae much reduced, frequently unrec- 

 ognizable, iv and v well separated; prolegs more or less reduced, often 

 absent when the true legs are absent; hooks, when present, in one or 

 two transverse or curved series, uniordinal, but sometimes with one of 

 the series doubled. Prolegs always absent on sixth segment of abdo- 

 men (characteristic of the family). The caterpillar in this stage is 

 always a miner, forming a more or less opaque mine (because the paren- 

 chyma is not eaten), which is often invisible from one surface of the 

 leaf. 



Full-grown larva strikingly different. Head but little flattened, with 

 normal mandibles and maxillae, and labium with spinneret. The bases 

 of the maxillae and labium long and slender. Prolegs always well 

 developed on third to fifth and last segments of abdomen, but wholly 

 absent on the sixth, the hooks as in the flat stage, but always more 

 or less developed. Body cylindrical, with minute but recognizable 

 setae. 



This type of caterpillar feeds on the parenchyma, either in an 

 inflated mine, more or less lined and puckered with silk, or externally 

 (skeletonizing the leaf) in a shelter which, in the typical forms takes 

 the form of a cone, with the larger end closed by folding over the end 

 of the leaf. In some species the cylindrical larva does not feed, but 

 immediately spins the cocoon. The cocoon is usually of white silk, 

 and is not woven in regular meshes. The mining species spin, as a rule, 

 within the mine. The external cocoons of Marmara and some species 

 of Acrocercops are ornamented with four groups of white bubbles, 

 which are ejected as a froth through slits cut in the cocoon after it 

 is spun; and soon set hard. 



The change from one type of larva to the other takes place at dif- 

 ferent stages in different genera, and even in members of the same 

 genus. In a couple of species of Acrocercops (Neurobathra Ely) the 

 change is gradual, covering two or three molts. 



