OF WASHINGTON. 247 



which bears centrally a minute seta or spine. This latter seems 

 to be the rudiment of what in certain Diptera is developed into a 

 t^th piercing seta. Viewed from beneath (IV" d") the hypopharynx 

 appears as a triangular piece (e) which closes against the pseudo- 

 sheaths of the maxillae, and large devaricating muscles. Viewed 

 from above it is seen to expand basally as two glistening surfaces 

 050 which apply to the lower face of the maxillae, just as the 

 similar face of the mandibles applies to the hypopharynx. 



The epipharynx and hypopharynx are intimately connected 

 with the clypeus and labrum and the labium respectively. The 

 mandibles and maxillae are, however, freely separable, with a little 

 care in dissection, and do not coalesce or come together in anyway, 

 but have smooth, glistening faces along the line of contact. 

 They are, however, so intimately associated that, while really 

 free, they have no lateral play upon each other, or but very little, 

 and do not perform at all the functions of the true biting mouth. 

 The shining inner surfaces of the hypo- and epipharynx indicate 

 that there may be a slight lateral motion, at least of the apical 

 expansion both of the mandibles and the maxillae ; but this 

 motion is probably confined to the more fleshy, inner portion of 

 these jaws, the chitinous exterior being probably fixed. 



With the mouth-parts all brought together in a state of rest, 

 as shown at figure i, the two expansions of the apex of the 

 mandibles with pseudo-sheaths apply together beneath and within 

 the labrum, and the mandibular setae, pass through the double 

 canal thus formed. The similar expansions of the maxillae also 

 apply very closely and project a little beyond the labrum, form 

 ing with the sheath-like projection from the apex of the latter 

 a short tube, which includes the bases of all the setae. The rela 

 tion of the parts described and the details of structure are accu 

 rately shown in the accompanying illustrations. 



Throughout all the higher families of the Hemiptera and 

 Homoptera the type of mouth structure detailed above is con 

 stant. In some of the families the labium varies in the number 

 of joints, having apparently four in the Aphididae, two in the 

 Aleyroclidae, and is obsolete or nearly so in the Coccidae. The 

 setae are, however, always present, and in the Coccidae are free. 

 The number of setae is constant, but in some of the lower fami 

 lies, particularly in the Aphididae and the Coccidae, the mandi 

 bular setae are very apt to be rather intimately united, so that 

 they do not separate readily, giving the appearance of but three 

 setae ; and in fact Buckton failed to recognize this union, and 

 said of aphides that they have but three setae instead of four. 



From the details of structure given above, with the accom 

 panying figures, which were based on dissections of a great 

 many insects, it is difficult to understand how Prof. Smith was 



