SANBORN : KANSAS APHIDID.E. O 



by its length, but does not afford such remarkable characteris- 

 tics as the antennae 



From a specific standpoint the latter appendages may be 

 used with more value than any other feature, and in regard to 

 which the following must be taken into consideration : The 

 number of segments,^ the total length, the length and color of 

 each segment, the number and shape of the sensoria on each 

 segment, and the union with the head. This union is care- 

 fully shown in each species illustrated, and also an enlarged 

 figure of the third segment, showing approximately the kind 

 and number of sensoria. 



Another characteristic to be mentioned in connection with 

 the head is the labium. (Plate I, fig. 1.) This is a greatly 

 enlarged mouth-part, which in some specimens is larger than 

 any other appendage. It has three or four segments, and in 

 its normal position lies on the ventral surface of the body be- 

 tween the legs, as shown in plate IV, figure 25. On the ventral 

 side of this is a canal, a cross-section of which is shown in 

 figure 5. In this groove lie the mandibular and maxillary 

 setir, a cross-section of which is shown in figure 6. 



The setie are all separate at their proximal ends, but in the 

 chitinous fold (fig. 3), which may be called the antelabial 

 sclerite, they are all approximated. The maxillary setae are 

 quite firmly locked with their concave sides opposite to each 

 other, thus forming a tube, a cross-section of which is shown, 

 taken from the first segment. (Plate I, fig. 'o, A.) These lie 

 on the median chitinized ridge on the floor of the canal, for 

 which see figures 3 and 6. On each side of this ridge is a simi- 

 lar chitinized line on which lie the mandibular setae. (Fig. 3.) 

 When the fioor is narrowed, as is done in feeding, the latter 

 chitinized areas are turned ventral side toward each other, thus 

 appressing the mandibular seta? with their concave sides oppo- 

 site, forming a tube in which are the maxillary setae."' Thus 

 each pair has a guide, in which they may slide lengthwise, and 

 drill into the tissues of the plant, from which the sap is con- 

 veyed to the assimilative organs of the insect through the tube 

 formed by the concavity of the maxillary setae. ^ 



1. The distal segment is not counted as sucli unless equal to or longer than the penulti- 

 mate. Exceptions, however, are cited. 



2. For treatise on the homopterous mouth-parts, see Walter J. Meek, K. U. Sci, Bull., vol. 

 XII, No. 9, 1903. 



3. Or, in other words, the labium ensheaths the mandibles, which in turn, by their concave 

 interior surfaces, encompass and hold in position the maxillnp. 



