1914 ENTOMOLOGICAL SOCIETY. 63 



and position in the legless species and by the presence of true thoracic legs in the 

 remainder. The larvae of the leaf-miners are usually depressed, the body is 

 moniliform with the head depressed and triangular in outline. 



The entire head and body, as is common with all insects, are covered by a 

 sheet of cuticle, which is thin and transparent in many species of Tenthredinoidea. 

 It is so transparent in some species that the form of the dorsal vessel or heart, the 

 alimentary canal in part, the air-tubes or tracheae, and the form and location of 

 a part of the masses of adipose tissue or fat, can be determined in the living animal. 



The head (Fig. 27), except as specified above, is globular in outline and the 

 mouth directed ventrad or caudad. The external head skeleton, the head capsule, 

 is strongly chitinized, fixed in form, and not readily changed from its natural 

 shape. The shape and hardness of the head distinguish it from the remainder 

 of the body. The only other difference worthy of note is found in the genus 

 Dimorphopteryx, where the head is distinctly triangular in outline. The head in 

 the Xyelidas, Pamphiliidge, and Tenthredinidae is fully exposed, but in Cephus and 

 Tremex (Fig. 10), a condition exists which is probably characteristic for all the 

 boring larvre. The cephalic part of the prothorax on the dorsal and lateral aspects 

 is produced into a broad fold which conceals the caudal part of the head. This 

 condition undoubtedly marks an early stage in the retraction of the head into the 

 thorax, so characteristic of many of the larvae of the higher Hymenoptera. The 

 parts of the head may be divided into two classes, the fixed parts and the movable 

 parts. 



The fixed parts of the head comprise all the immovable parts of the head 

 skeleton. The surface of the head skeleton may be entirely glabrous or with a few 

 scattered setse about the ventral margin as in Pamphilius or with numerous pro- 

 miscuously arranged short setae, more abundant on the ventral half of the head, as 

 in Tremex, Lophyrus, Caliroa, Ahia, and Croesiis or with long seta; as in Pteronus 

 or with numerous very long setae as in T rid lio campus. The surface may also be 

 polished, opaque, or roughened. If the surface is roughened, there can usually be 

 recognized many closely placed quadrangular or oval areas with one or more cen- 

 tral brownish spots. These areas are distinct in Cimhex, Empria, Lagium, and 

 Lygaeonematus. They probably mark the location and extent of the hypodermal 

 cells located beneath the cuticle. 



There is a large opening in the caudal aspect of the head (Figs, t and 5, of) 

 the occipital foramen, through which the alimentary canal and other organs pass 

 from the head to the thorax. This opening can not be identified, except in a 

 general way, until the head has been removed from the thorax. 



In the heads of adult generalized insects, as the cockroach, there is a suture 

 (Figs. 2, 3 and 9, e), the epicranial suture, extending from the caudal aspect of the 

 head along the meson to the middle of the cephalic aspect, where it divides into 

 two arms, which extend toward the compound eyes, making a figure shaped like 

 an inverted Y. This suture can be identified on the heads of most Tenthredinoidea 

 as a faint line, like a break in the cuticle in brown or black colored heads and as 

 a slightly depressed line in opaque white colored heads. The compound eyes are 

 wanting in larvae and the arms of the Y after making a broad curve (Fig. 3, e) 

 extend directly to the ventral margin of the head capsule. The exact course of 

 the arms of the epicranial suture varies but little in diiTerent species. The stem 

 of this suture originates at the occipital foramen (Figs. 4 and 5, of). In Tremex 

 (Fig. 10), all parts of the epicranial suture are wanting. 



