20 ILLINOIS BIOLOGICAL MONOGRAPHS (338 



according to the genus. The antennae of the Tenthredinidae (Figs- 

 145, 147, 149, 150, 153) apparently represent a specialization from those of 

 the Xyelidae. They are much shorter and vary in number of segments 

 from one to five. The antennae vary in shape and are conical in the 

 Emphytinae and other generalized subfamilies, with five ring-like or 

 limpet-shaped segments, with four more or less irregular, incomplete, often 

 partly fused segments in the Nematinae (Fig. 145), or flattened and fused 

 into a single segment in the Schizocerinae or button-like and one-segmented 

 in the Cimbicinae, Fenusinae, and Metallus (Fig. 147), or subcorneal or 

 irregular as in some Nematinae and Phlebatrophia (Fig. 150). When 

 the antennae consist of five segments, they are usually cylindro-conical 

 and remarkably uniform in shape. The antennal segments are usually 

 strongly chitinized, more or less ring-like, successively smaller in diameter, 

 and the distal segment is conical or occasionally erect and peg-like as in the 

 Diprioninae. The segments do not always form a complete ring; one 

 side may be reduced to a mere line, or be entirely wanting as in some 

 Nematinae, in which cases the segment is said to be incomplete. Some- 

 times fusion of all or some of the segments may take place. Certain 

 segments are sometimes setiferous and also bear some sensoria. The 

 number of segments is constant for a subfamily. The relative length and 

 shape of the segments vary, but are constant in species in some cases, and 

 in others constant in genera. The antennae of the Cephidae are small, 

 with four or five segments, while in the Xiphydriidae they are three- 

 segmented and in the Siricidae and Oryssidae single-segmented. It is 

 possible, therefore, to arrange the families of Tenthredinoidea in an as- 

 cending series according to the number and size of the segments of the 

 antennae. The tenacity of the antennae is well Illustrated in the Oryssidae, 

 which in spite of the extreme modification of other structures still retains 

 one-segmented antennae. 



Mouth-parts. — The larvae of the Tenthredinoidea possess well-devel- 

 oped mandibulate mouth-parts. They include the mandibles, maxillae, 

 and labium, and are remarkably uniform and constant in structure in the 

 different families. The modifications take place in the relative size of 

 parts and in the number of segments of the articulated parts. 



Mandibles. — The mandibles (rnd) are always present, and are typically 

 thick, strongly chitinized, and sharply dentate, the dextral dissimilar to 

 the sinistral in the number and shape of the dentes, and in having one or 

 two and occasionally more mandibular setae on the lateral aspect. The 

 number and arrangement of the dentes, the number of mandibular setae, 

 and the relative size and shape of the mandibles are constant for certain 

 genera. The mandibles of the Schizocerinae are rather thin and flattened, 

 and in Phlebatrophia very thin and elongated with one triangular blade- 



