12 ILUSOIS BIOLOGICAL MONOGRAPHS |254 



separation of the labium from the cervix. Consequently, this appendage is 

 finally borne by the postgenae instead of by the cervix, which represents 

 the segment to which the labium morphologically belongs. A parallel 

 specialization is exhibited by the adults of certain aculeate Hymenoptera. 



In the more generalized lepidopterous larvae of the Cossidae, Pyralidi- 

 dae, and Tortricidae examined, a few species of each, we find the post- 

 genae quite widely separated (Figs. 3, 4, 5). Young larvae of Thyrid- 

 opteryx ephemeraeformis from the first to the fourth instars (Fig. 6) also 

 reveal this condition, although these sclerites meet on the meson in the full- 

 grown larvae (Fig. 7), a recapitulation to be treated later in the section on 

 postembryology. Secondary sclerites are sometimes formed by a chitin- 

 ization of this membrane (Fig. 4). Frequently each postgena (Fig. 5) is 

 divided by an oblique secondary suture. In hesperiid larvae the postgenae 

 are exceptionally widely separated, the area (Fig. 8) between them being 

 uniformly and heavily chitinized, resembling the gula of the Coleoptera. 

 Larvae of several families have retained but a narrow strip of cervacoria 

 between the postgenae. In representatives of the Sphingidae, Saturniidae, 

 Lymantriidae, and Pieridae examined, they are separated only by a suture. 

 The Noctuidae (Figs. 9-12) present the same condition most frequently, 

 although a narrow strip of coria often persists. 



In certain of the more specialized families, notably the Saturniidae 

 and Noctuidae, the cervix caudad of the postgenae has developed a vary- 

 ing number of folds, some of which have become flattened one onto the 

 other, chitinized, and cemented to the postgenae, where they now resemble 

 sclerites. This peculiar condition appears to reach its height in the former 

 family, some of whose larvae have several such folds superimposed upon 

 one another and apparently fused mto a thick, heavily chitinized sclerite, 

 which lies flat upon the postgenae. In the Noctuidae the most cephalic 

 fold only is chitinized and fastened down in this manner, where it assumes a 

 bilobed form. The dorsal portion of this cervical fold is covered by the 

 membranous one which follows it, exposing the brown, flat, crescent- 

 shaped ends of the bilobed first fold, so that they appear as divisions of 

 the postgenae, one on each side of the meson. 



In the Noctuidae part of the secondary infolding which extends around 

 the dorsal portion of the margin of the foramen separates on each side a cres- 

 cent-shaped secondary sclerite (Fig. 9) from the remainder of the vertex. 

 The pleural portion of the neck-membrane is fastened to this sclerite. 



ENDOSKELETON 



The tentorium of lepidopterous larvae (Figs. 3>, 13, 14) is very greatly 

 reduced. It is unfit for the function of support generally performed by 

 this structure. In correlation with this reduction a large number of large, 

 heavily chitinized infoldings have developed along certain primary and 



