FAM. MEMBRACID^ 



21 



anteiior margin of the sclerite and projects forward, engaging the posterior margin of the pronotum. 

 It is found in the great majority of the genera of the family, but not in all. Its function would appear 

 to be the interlocking of the pro- and mesothorax by an external mechanical means. It has been noted 

 that internally these segments are but weakly joined, the intersegmental membrane being fragile and 

 easily torn. The shape and position of the hook vary but little, and in all cases the process is close 

 to the wing base. It has not been found to vary within a genus. 



The trochantin of the metathorax is much larger than this sclerite in either of the other two 

 thoracic segments. It shows the same general shape as in the other segments — an elongated wedge 

 or triangle — but is longer, wider, and thicker. It forms part of the lateral margin of the coxal cavity 

 and joins the cephalic bar of the sternum at its lateral extremity. No evidence has been found of either a 

 transverse or a longitudinal division of this sclerite, and nothing that would suggest the « trocbantinus 

 niajor » and the « trochantinus minor » which Crampton (igog) has found in other ordeis of insects. 



In a very few instances small thickenings have been found in the coxal region which suggest vesti- 

 gial sclerites. So rare, however, have been such conditions that they cannot be said to be of importance 

 in the family. In by far the larger number of forms the sclerites have been only of the number pre- 

 viously mentioned and no accessory trochantinal or accessory coxal sclerites are present. Neither does 

 there appear to be any structure of a similar nature concealed by or hidden within the coxas, as has 

 been shown to be the case in some other hexapods. The metathoracic spiracle is located just cephalad 

 of the upperangle of the episternum, in about thesame relative position as that of the preceding segment. 

 It will be seen that only two spiracles are found on each lateral surface of the thorax. Careful examination 

 of the prothorax has been made for a hke structure, with negative resuUs. A prominent spiracle is 

 located just caudad of the metathoracic pleuron and superficially appears to be a part of that segment; 

 but, as will be noted later, this properly belongs to the first abdominal segment. 



The sternum of the metathorax is much smaller than that of the mesothorax, and, though its 

 configuration suggests that it may be composed of two or more sclerites, absolutely no evidence has 

 been found to bear out such an inference. Neither the nymphal nor the adult forms show sutures 

 indicative of such development, and it seems necessary to discuss this part of the segment as a single 



fx)ssa 



yvofum 



jt/oimeron 



'£p/\sfernum 



~^Troc/ianfin 



'-A/feJonofum 



^pimeron Z 



i-fp/meron f 

 P/eura/ sufure 

 y "fjo/jfernum 

 rroc/tanfin 



Mefanofuni 

 ' ^pimeron f 



EpimeranZ 

 ^'£pi\sfernum f 

 ■:.ip/jfernum 2 

 TrocAanfin 



FiG. 3. — Thoracic structures 



sclerite. In shape the metasternum is roughly a transverse « II », the openings at the end of the 

 figure representing the coxal cavities. The sclerite thus encloses the mesal curve and one-half of the 

 cephalic and caudal margins of these cavities. The cephahc bar is shghtly swollen ventrad, the middle 

 connection is flat, and the caudal bar, again, is somewhat swollen. As in the case of the preceding 

 segment, a strictly ventral aspect of the metathorax shows more than the sternum. The lateral edge 

 of the body is formed, not by a flat, perpendicular pleural wall, but by the junction of the upper pleuron 

 with the lateral ventral margin of the metanotum. The ventral view, therefore, shows the pleura as 

 far dorsad as the wings. 



