NO. 1310. NORTH AMERICAN TIIYSANOPTERA— HINDS. 93 



tips, where they are quite sharply pointed and strongly chitinized, and 

 may reach sliohtly beyond the labrum. At about the middle point of 

 the side of each maxilla i.s borne a two or thi-eo segmented palpus. 

 In the xEolothripida> this is always three seu-mented and o'eniculate; 

 in the Thripida> it is composed of two or three approximately equal 

 seg-ments and is straight, the segments being cylindrical hut decreas- 

 ing successively in diameter; in the Phloeothripidjv it is always two 

 segmented and the segments are very unequal in length, the basal one 

 being short and rounded while the second is long, slender, and cylin- 

 drical. The terminal segment is in all cases provided with a few touch 

 bristles which are but rarely distinctly and easily visible. 



Lah!i()n.—Th& labium is believed to be formed by the union of the 

 second pair of maxiil». and in many insects evidence of this can be 

 seen, but in the Thysanoptera there is no visible suture along the 

 median line, though sometimes a deep median notch is present at the 

 tip. It forms the hind wall of the mouth cone and is, as a rule, con- 

 siderably broader at the tip than the other parts. In many species, of 

 Tubulifera especially, it is very broad and heavy at the tip, but in 

 others it is narrowed and the whole mouth cone is then usually elon- 

 gated and pointed. Standing closely together, each upon a membra- 

 nous space a little to one side of the middle of the tip, are the two or 

 four segmented, cylindrical, labial palpi. The maximum number of 

 segments is here found also in the ^EolothripidiB, and the minimum 

 number in the Thripidie and Phhjeothripida?. Around the tips of the 

 labial palpi are borne a few touch bristles similar to those upon the 

 maxillary palpi. 



Within the hollow cone formed by the parts just described lie the 

 protrusile, piercing organs of the Thysanopteran mouth. These 

 organs are three in number and of two kinds. Their homologies have 

 been confused bv various writers. 



MandMr. — This is the large, unpaii'ed, piercing spine lying on the 

 left side in the mouth cavity. It has been variously interpreted as 

 epipharynx, mouth spine, etc. In the right side of the head there is 

 no trace, or but a mere vestige, of the corresponding organ. The 

 a])sence of the rig-ht mandible appears to be closely correlated to all 

 the asymmetry of the mouth parts of these insects. The mandible con- 

 sists of two parts, though these are not separated in any way. The 

 large bulbous base appears to be mostly muscular and is attached to the 

 endocranial thickening behind the loft eye close to the angle which is 

 made by the endocratiium at this point, and about in line with the 

 branch from this thickening running to the left eye in Terebrantia, 

 which branch thus appears to form a strong brace. On the right side 

 the absence of this endocranial branch is doubtless due to the non- 

 development of the right mandible, and the labrum has grown out 

 farther on the right side to take the place in some measure of the 



