NO. 1310. NORTH AMERICAN THYSANOPTERA— HINDS. 95 



chewing^ their food to any degree, though it has been stated that par- 

 ticles of leaf tissue have been detected in their excrement. This ma}^ 

 be accounted for by the fact that the mouth parts are quite strongly 

 chitinized at their tips, and so may serve, to some extent, to rasp 

 or tear the tissues, small particles of which may be drawn into the 

 alimentary canal with the sap. 



THORAX. 



(Plate XI, figs. 116-119, 125-127.) 



The thorax is composed of three distinct segments, each of which is 

 well developed. The prothorax is separated from the mesothorax by 

 a deep constriction and is freely movable. The other thoracic seg- 

 ments are closely grown together and form what is conveniently 

 called the pterothorax. The larval thorax shows no particular chitin- 

 ized plates and its whole structure and the arrangement and develop- 

 ment of the spines have been but little studied. 



Most previous descriptions of the thoracic structure of these insects 

 have been very brief. Unfortunately Dr. Uzel has given the entire 

 anatomical part of his monograph in Hungarian, and therefore his 

 description of the thorax has not been available. It is evident that 

 there is considerable variation in the thoracic structures in different 

 species, and it may be that when carefully worked out these parts will 

 be found to have considerable importance in classification, whereas 

 they have not been used in this way heretofore. A general descrip- 

 tion of the parts of the thorax is difficult to give and must be subject 

 to much modification in many species as the homologies of some parts 

 are not well established. 



Prothora.r.~Th\s segment is as wide or wider than the head and 

 varies much in its proportions and form. It is rarelv much longer 

 than wide, usually exceeds the mesothorax in length, and in most cases 

 approximately equals the metathorax. The form in the Terebrantia 

 IS usually more or less rectangular, with the sides and hind edge espe- 

 cially somewhat rounded. This form is also found in some Tubulifera, 

 but as a rule among them the thorax is trapezoidal, being much wider 

 at the hind edge than at the front. This trapezoidal form appears to 

 be closely related to the development of the fore legs, since in the 

 genus ChiTothnj>s where the fore legs are extremelv thickened there 

 IS found the same form of prothorax as in the Tubuliferan genera 

 where the fore femora are also enlarged. 



The pronotum is strongly chitinized. In the Thripida- it is usually 

 more or less transversely striated and often bears numerous small 

 spmes. In the other families it is generally smooth. 



In most Thysanoptera the prothorax bears long conspicuous spines, 

 the number and arrangement of which are much used in classification. 

 Ihese stand usually around the outside of the pronotum— one or two 



