462 SYNOPTIC COLLECTION. 



pupate. There it spins a silken cocoon (fig. 4) that is 

 black inside and out, and changes to a pupa (fig. 5). 

 The latter is provided with a horn-like process on its head 

 (see fig. 5) for opening a way out of the cocoon and with 

 abdominal hook-like spines for working its way to the 

 surface where it transforms to the winged adult (fig. 6, J ; 



fig. 7, ?) 



The adults of this family. Sesiidae, have the larger part 

 of one or both pairs of wings free from scales (No. 1172, 

 Sesia thysbe Fabr). The latter are found, however, on 

 the veins and the edges of the wings. The bristles of the 

 frenulum in the female are consolidated into one organ 

 as in the male. 



Among the frenulum conservors are the Geometrids 

 whose larvae appear to measure the surface over which 

 they walk. It is probable that the caterpillars of the 

 ancient Geometrids had several pairs of prop-legs like the 

 larvae of most living Lepicloptera, but when the Geome- 

 trids acquired the habit of walking by looping the body, 

 there would be no need of any of the prop-legs excepting 

 the last pair or two and disuse would tend to bring about 

 reduction and loss of these organs. 



The canker caterpillar, so disastrous to shade and fruit 

 trees, is a Geometer. It occurs in the spring form, 

 Paleacrita vernata Peck, and the fall form, Anisopteryx 

 pometaria Harr. (No. 1173, $ , 9 ). The position that 

 the quiet larva often takes causes it to resemble a twig 

 and this is doubtless a means of protection. When walk- 

 ing it brings the posterior end of its body forward towards 

 the head end and takes firm hold of the twig by its prop- 

 legs, thereby looping its body ; it then stretches out the 

 forward end and takes hold by the thoracic legs when the 

 posterior part is again brought forward. 



The larvae of some of the Noctuidae or owlet moths 

 do great damage to grass and crops. One well known 

 species is the northern army caterpillar, Leucania uni- 

 puncta Haw. (No. 1174, larva and adult). It is probable 



