THE MOUTH-PARTS OF THE THYSANOPTERA. 25 



felt about calling attention to it. After verifying obser- 

 vations again and again on several species of two genera, 

 by dissection and other means, I am persuaded to publish 

 a brief notice of it in the hope of getting further light, and 

 also with a view to learning how general the peculiarity 

 referred to is for the group, a matter which I am not able 

 to decide from the material now in my possession. 



The statements generally made with reference to the 

 structure of the mouth are, that it is fitted for taking liquid 

 food ; that the mandibles are long, slender, styliform, and 

 slightly swollen at the base ; that the maxillae are triangu- 

 lar (in outline), pointed, and bear palpi; and that the la- 

 brum and the labium are well developed, the latter with 

 palpi. 



In all the examples of the order which I have examined, 

 the labium, with palpi of two segments, agreed closely 

 with the published descriptions and figures. 



The triangular parts (the maxillae of authors), each 

 with a palpus, sometimes of two, sometimes of three seg- 

 ments, have been easily recognized from the descriptions, 

 but instead of being pointed they are slightly swollen at 

 the tip, and the margins there project above one surface 

 as chitinous rims, leaving a groove between them. 



The labrum, in the species dissected, is not a symmet- 

 rical organ, but its two sides are quite different in shape. 



On the right side its lateral margin is the more oblique 

 relative to the middle line, and it extends consequently 

 farther out on this side at its base. The lateral margin 

 of the left side is more nearly parallel with the middle 

 line, and the labrum does not extend so far out at the 

 base. Otherwise the labrum agrees with published de- 

 scriptions. 



In every example dissected there is at the left of the 

 labrum, and apparently articulating with the epicranium, 



ESSEX INST. BULLETIN, VOL. XXII 2* 



