METAZOA INSECTA. 461 



trunk or branches where it can spend the winter. Several 

 of these attached hibernating larvae are seen on the 

 branch in fig. 2, and the larva with the case removed in 

 fig. 4. In the spring the larva changes to a pupa (fig. 5) 

 and finally becomes the winged adult (fig. 6). 



The habit of leaf mining in the larval state has brought 

 about a reduction of the locomotor organs of Coptodisca, 

 so that, according to Clemens, 1 there are no thoracic legs 

 but rather cup-like depressions on both the ventral and 

 dorsal side which are capable of contraction and expan- 

 sion. Neither are there prop-legs, but in their places are 

 folds of the integument which act as substitutes for these 

 organs. 



This tendency towards reduction and loss of the legs is 

 carried so far that in Phyllocnistis, according to the same 

 author, 2 not only are there no legs nor prop-legs, but vol- 

 untary motion has almost wholly ceased. 



The Sesiidae or clear-winged moths are represented 

 by Melittia satyriniformis Hbn. (PL 1171, figs. 1-7). 

 This genus is especially interesting since the newly 

 hatched larva (fig. i) is similar to the Thysanuriform 

 stage of the more primitive insects. The shape of its 

 body, the three pairs of legs which, though small, are 

 plainly seen from above extending outward on either side 

 of the thorax, the bristles at the posterior end of the body, 

 are all characters suggestive of the Thysanura and the 

 Thysanuriform stage of development. This stage, how- 

 ever, is quickly passed over, so that the half-grown larva 

 (fig. 2) has the caterpillar form. The mature larva (fig. 

 3) is a borer in the hollow stems of the squash vine, and 

 it shows adaptation to its habitat by the reduced condition 

 of the legs. 



Like manv beetles, Melittia descends into the earth to 



'U.S. Dep. Agric., Rep. of Entomologist, by Comstock, 1879, 

 p. 213. 



2 Tineina of N. A., 1872, p. 25. 



