18 ILLINOIS BIOLOGICAL MONOGRAPHS [260 



that of the saw-fly larva figured by Berlese and Yuasa is so labeled. The 

 absence of these sclerites in many lepidopterous larvae together with the 

 fact that they are generally widely separated by the membrane and never 

 constitute a single piece indicates that they represent merely two strongly 

 chitinized areas of the submcntum. They seem to have developed in cor- 

 relation with the arms of the subcardines, whose chitinized portions lie 

 adjacent to these plates of the submentum. The arms extend beneath the 

 chitinized areas of the submentum and serve for the attachment of muscles, 

 hence the advantage of these chitinous plates in the membrane adjacent to 

 them. The membranous portion of the submentum always bears a pair of 

 large setae. 



The mentum is usually reduced or undifferentiated in specialized labia, 

 the submentum being well developed and the stipulae always present. In 

 caterpillars the mentum is not present as a distinct area, being presumably 

 fused with the stipulae, which is the condition apparently found in all 

 coleopterous, trichopterous, and saw-fly larvae. In those of the Lepidop- 

 tera the stipulae usually consist of a proximal chitinized ring and a distal 

 membranous portion, which bears the palpigers and the vestigial glossae 

 on which the spinneret is located. This area is referred to by Forbes but not 

 named, whereas Berlese and Dampf consider it as the mentum. Just 

 proximad of the proximal end of the spinneret on the caudal aspect there is 

 a pair of minute setae. 



The chitinized portion of the palpiger is typically an incomplete ring, 

 its mesal and distal portions being membranous. Dampf has suggested 

 that this structure may represent the basal segment of the palpus, in which 

 case the palpiger must be regarded as undifferentiated. It varies much in 

 width and shape throughout the order, resembling in Enocrania and Adela 

 a basal segment of the palpus. In the Noctuidae it is not closely associated 

 with this appendage, assuming the form of a semicircular sclerite lying in 

 the membrane distad of a stipula. The mesal end of the caudal aspect of 

 this semicircular sclerite is provided with two large sensoria. A reduction of 

 the chitinized area mesad of the sensoria, which has frequently taken place 

 throughout the order, has left them on the mesal end of the sclerite, where 

 they remain surrounded partially or entirely by chitinized rings, the rem- 

 nants of a more general chitinization. In the Noctuidae, where this reduc- 

 tion is usually marked, the distal sensorium is rarely completely sur- 

 rounded, the ring being typically broken on its mesal side. 



The two-segmented palpus has been correctly named by previous 

 •workers. The membrane which bears it within the semi-circular palpiger 

 is generally wide, allowing free movement of this appendage. Its proximal 

 segment is cylindrical, varying from stout to slender, the former shape being 

 the most usual in the order and typical for the Noctuidae. It bears a 

 terminal seta usually laterad of the distal segment, a minute cylinder 



