6ii THE KEPORT OF THE No. 36 



its ventral margin; in some species the emargination is so deep as to almost divide 

 it into two pieces. The labrum varies considerable in size and shape. 



In the larvae of insects with a complete metamorphosis, the eyes, if present, are 

 represented by one or more simple eyes or ocelli, placed in a group on each lateral 

 aspect of the head. The portion of the head capsule bearing this group of simple 

 eyes is usually different in color or in sculpture. In order to differentiate this 

 region from the adjacent parts, it has heen designated as the ocularium (Fig. 9, ol). 

 The ocularium in the Tenthredinoidea bears a single ocellus (Fig. 3, o). The 

 presence of a single ocellus on each side of the head is the most useful character for 

 differentiating the larvae of the Tenthredinoidea from those of the Lepidoptera, 

 which usually have five or six. 



Ill certain larvae the mouth is directed to the front and certain of the neck 

 pieces fill the space on the ventral aspect of the head. The area, designated as 

 the gula, is wanting in the larvae of the Tenthdelinoidea. 



The external head skeleton is supported by three pairs of pillars, which extend 

 in different directions, and are known as the tentorium. The postgenae are con- 

 nected by a transverse bar, which extends within the cavit}' of the head. This bar 

 is a part of the tentorium (Figs. 4 and 5, tn). It is known as the body of the 

 tentorium. The place of attachment of two of the pairs of arms of the tentorium 

 has already been described, the third is attached near the ends of the body of the 

 tentorium (Fig. 5, tp). 



The movable parts of the head comprise the antennae, the mandibles, the 

 maxillae, and the labium. 



The antennae are inserted in round depressions, the antennal sockets, located 

 on each side of the head near the ocularium. In Pamphilius (Fig. 2, as) they are 

 placed between and a little above the ocularium and the front; in Cimbex (Fig. 3, 

 at), between the ocularium and the ventral margin of the vertex, their usual loca- 

 tion in the larvas of the Tethredinidae ; and in Tremex (Fig. 10, at), they are located 

 laterad of the ocellus, the ocellus being placed between the antennal sockets and the 

 front. 



The antennal sockets (Fig. 2„ as), are surrounded by a membranous ring in 

 the Pamphiliidse, but in all the other larvae examined they are completely filled by 

 the proximal end of the antenna?. The antennre of the Pamphiliidae (Figs. 2 and 9, 

 at), are the most generalized in form. In this family they consist of seven segments 

 and their length is equal to one-half the width of the head. In no other Tenth- 

 redinoidea examined do they approximate such a condition, while they may consist 

 of as many as five segments, yet they are hardly more than mere tubercles in length. 

 The fusion and reduction of the segments of the antennae are gradual and are of 

 value in showing the sequence of the groups. In the Emphytinae, Dolerinae, Selan- 

 driina3 (Fig. 16), and some others, they consist of five ring-like segments; in the 

 Nematinae (Fig. 18), they consist of transverse plates that appear to be closely 

 appressed to the surface of the antennal socket, each plate is supplied with sensory 

 setae and represents an antennal segment; in the Acordulecerinse there are only two 

 of these plates; and in Cimbex (Fig. 14), they are reduced to mere blunt stubs. 



As already noted, one of the condyles of each mandible articulates in an ace- 

 tabulum in an antecoxal piece (Fis:s. 2 and 3), the other condyle articulates in an 

 acetabulum on the caudal aspect of the head at the ventral end of the suture separat- 

 ing the gena and postgena (Figs. 4 and 5). The mesal margin of each mandible 

 closes under the edge of the labrum and clypeus, is provided with prominent teeth, 

 and together with the clypeus and labrum closes the ventral part of the head. 

 (Fig. 9). 



