10 ILLINOIS BIOLOGICAL MONOGRAPHS (252 



antacoriae divide each epicranial arm into two portions, the ventral being 

 known as the fronto-genal suture. These are homologous, therefore, with 

 the ventral portions of the epicranial arms of larvae. The two large 

 sclerites which are separated by the epicranial stem, lie dorsad of the arms, 

 comprise the greater part of the head-capsule, and make up the vertex. 

 Its apparent large size in larvae is due to the absence of compound eyes. 

 Since the occipital sutures are undeveloped, the caudal extent of the vertex 

 is indefinite. It has been customary to refer to the fused vertex, occiput 

 and postgenae as the epicranium. The vertex of lepidopterous larvae does 

 not differ from larval vertices generally in bearing the ocellarae, and an- 

 tennarae. The antennarae, which bear the antennae, are distinct in the 

 noctuid larvae, a generalized condition found typically in the adults 

 of the more primitive orders. 



There is but one marked indication of fundamental structural special- 

 ization visible externally on the vertex of lepidopterous larvae. The ad- 

 frontal sutures, which have developed solely in the larvae of this order, 

 run subparallel to the epicranial arms, dividing the vertex on each side into 

 two portions, the mesal one being the well known adfrontal area. Hereto- 

 fore, these secondary adfrontal sutures have been generally regarded as 

 the epicranial arms and vice versa. Heinrich agrees with Dampf in his 

 assertion that the adfrontal sclerites are a part of the front, regarding the 

 sutures between the front and adfrontals as secondary infoldings. Both 

 of these investigators were aware that the pretentoria invaginate at the 

 bottoms of these infoldings, a point demonstrated by Berlese one year 

 previous to the publication of Dampf's paper on case-bearing larvae. The 

 interpretation of these authors necessitates the supposition that the pre- 

 tentorinae were originally located on the front some distance mesad of the 

 epicranial arms and that they were subsequently involved by this supposed- 

 ly secondary infolding, which resulted in their present position. We shall 

 present evidence which appears to show conclusively that the mesal 

 sutures are the epicranial arms and that the lateral ones are secondarily 

 developed. 



In the first place, the pretentorinae of the larvae of other orders, so 

 far as we know, are associated with the epicranial arms. They are rarely 

 situated on the front removed from primary sutures. IMoreover, the epi- 

 cranial stem in lepidopterous larvae, unquestionably a primary structure, 

 is followed internally (Fig. 1) by a deep infolding, which is continuous with 

 and exactly like those of the mesal sutures which bear the pretentorinae. 

 It seems highly improbable that the former suture should be primary and 

 the latter secondary, when their infoldings are continuous. The fronto- 

 clypeal suture, also a primary suture beyond a doubt, is expressed internally 

 by a similar infolding. This suture extends between the mesal sutures and 

 does not traverse the adfrontal sclerites terminating at the lateral sutures, 



