OF WASHINGTON. 243 



The results hereinafter detailed are based upon dissections of 

 the periodical cicada, which, on account of* its large size and 

 the abundance of material available, immediately suggested it 

 self as a convenient subject for study. 



All of the main parts of the mouth of the biting insect occur 

 in the mouth of the cicada. Beginning anteriorly and naming 

 them in the order of their occurrence, they are : (i) the clypeus, 

 (2) the labrum, (3) the mandibles (the inner part of which are 

 the upper and stronger setae), (4) the mtixillas, with which belong 

 the two following and more slender setae, and (5) the labium or 

 sheath beneath. Within the mouth are the epipharnyx, project- 



are short and inserted at a distance apart, and have a horizontal motion, 

 the action is that of biting; when, on the other hand, the lateral pieces 

 are elongated, originating near together and having a longitudinal motion 

 (by means of strong, elongated muscles at their base), the action 

 is that of sucking." He suggests the terms dacnostomata (biting mouth) 

 and antliostomata (sucking mouth) to express the characteristics of the 

 two groups, without involving the contradiction suggested by the terms 

 in use. 



Adopting for convenience the old comprehensive ordinal names, the 

 Dacnostomata comprise the Coleoptera, the Orthoptera, the Neuroptera 

 and the Hymenoptera ; and the Antliostomata the Diptera, Hemiptera, and 

 Lepidoptera. 



To appreciate the modification of mouth-parts in the orders of sucking 

 insects, the main features of the biting mouth may be noted. They com 

 prise two pairs of laterally-working, shear-like jaws (mandibles and max 

 illae), inclosed above and beneath respectively by the upper lip (labrum), 

 the lower lip (labium), the latter bearing on its inner surface the tongue 

 (ligula) with sometimes, also, a false tongue-like appendage originating 

 from the roof of the mouth, or labrum. The principal modifications of 

 this mouth structure in sucking insects are as follows : In the Hemiptera 

 the four jaws are elongate, setiform, and are inclosed within the under 

 lip, forming what has been termed the promuscis or beak. In the Diptera 

 (in the more fully developed mouth) the upper lip, the four jaws, and the 

 tongue are elongate, setiform, and inclosed within the elongated enlarged 

 lower lip, forming what has been known as the proboscis or rostrum, ap 

 proaching very closely the type of mouth found in the Hemiptera. In 

 the Lepidoptera the outer lobes (galese) of the maxillae only are elon 

 gated, and closely applied and interlocked to form the spiral tongue or 

 sucking tube, the madibles, labium, and other parts remaining rudimen 

 tary or not specially developed. Numerous and important variations in 

 structure occur in each order, as, for illustration, most.Hymenoptera are 

 somewhat intermediate between the biting and sucking groups, and in 

 the Lepedioptera the larvae are biting and in the Hemerobidae (Neurop 

 tera) the larvae are sucking. 



