253] KOCTUID LARVAE— RIPLEY 11 



as it should if the lateral sutures were the epicranial arms. Postembryo- 

 logical evidence offers still stronger support to this interpretation. The 

 lateral sutures are not distinct in noctuid larvae in instars earlier than the 

 penultimate. So far as we have been able to ascertain the earlier instars of 

 all lepidopterous larvae lack the adfrontal area, although this point appears 

 to have been generally overlooked. It is not always distinctly separated 

 from the vertex even in full grown larvae. The accurate morphologist, 

 Berlese, shows no trace of it in his figures of the ectal and ental aspects 

 of the larval head of Acherontia. These are secondary structures appearing 

 relatively late in their postembryonic development. Therefore, they can- 

 not be homologous with the epicranial arms, which represent the lines of 

 dorsal closure on each side of the so-called unpaired appendage in the em- 

 bryonic development. 



The triangular front between the epicranial arms is separated from 

 the postclypeus by a more or less distinct frontoclj-peal suture. This 

 suture in the more primitive insects terminates near the precoUae. In 

 lepidopterous larvae this suture has migrated dorsad, its ends joining the 

 epicranial arms at points considerably removed from the articulations of 

 the mandibles, a condition frequently found in specialized insects. Where- 

 as the position of this suture probably denotes specialization, its well 

 developed condition, on the other hand, is to be regarded as a general- 

 ization, since it is frequently lost in both larvae and adults of various orders. 

 It is sometimes not traceable externally in noctuid larvae and is rarely as 

 prominent as the ch-peal suture, which marks the di\'ision between the 

 preclj-peus and the postch-peus. This division also denotes a primitive 

 condition, as is evident from a general study of insect morphology. The 

 labrum of the noctuid larva always presents the bilobed shape character- 

 istic of lepidopterous larvae. 



The caudal aspect of the lepidopterous larval head shows pronounced 

 and varied specialization. It seems odd that this region, which perhaps 

 offers points of greater morphological interest than any other part of the 

 head, should have been so utterly neglected. Prominent secondary sut- 

 ures extend dorsad from the mesal edge of the postcoilae, marking the 

 location of deep infoldings. The position of these sutures with reference to 

 the postcoilae precludes their being homologous wth the occipital sutures, 

 which are always situated laterad of the postcoilae and are universally 

 borne by the postgenae. It is convenient to refer to the region mesad of 

 these sutures as postgenae, although it should be remembered that the 

 lateral extent of the true postgenae is undefined, the occipital sutures 

 being undeveloped. In all but certain of the more specialized orders the 

 postgenae in both larval and adult insects are widely separated by the 

 cervix. In lepidopterous larvae there has been a tendency toward the 

 extension mesad and an ultimate fusion of the postgenae, resulting in a 



