96 ENTOMOLOGICAL SOCIETY 



The microthorax, or presumed segment formed by the neck 

 sclerites, is a much neglected part of insect anatomy. It has 

 recently, however, been well studied by Verhoeff and prob- 

 ably made too much of by him. It is best developed in the 

 Blattidae, Mantidge, Gryllidse, and Euplexoptera, and is now 

 usually regarded as a rudimentary segment of the thorax. 

 Many embryologists claim that the second maxillae are its 

 appendages and that the labium, resulting from the fusion of 

 the latter, has secondarily moved forward and become an ap- 

 parent appendage of the head. The articulation of the sub- 

 mentum in adults of Mantidae and Gryllidse certainly gives 

 support to this idea, for in these insects (fig. i) the labium is 

 clearly suspended at its basal angles, not from the head but 

 from the sternal and pleural sclerites of the microthorax. In 

 most of the higher insects the microthoracic sclerites are rudi- 

 mentary or absent and the labium is suspended from the head. 

 In Coleoptera and in some other forms the submentum is far 

 forward on the head and the cranium is closed behind it either 

 by a gular sclerite or by the approximation of the lateral walls. 

 In all Euplexoptera the microthorax is well developed and in 

 Spongophora at least the submentum is distinctly articulated to 

 the cranium (fig. 13) a considerable distance in front of the 

 neck sclerites. Here the sternal plates of the microthorax are 

 so large as to be strongly suggestive of the notion that they 

 have followed the labium forward in the Coleoptera and 

 formed the gula. The pleural and sternal sclerites of the micro- 

 thorax are always much more developed than the dorsal. The 

 last generally consist of two small nledian or convergent plates. 

 Verhoeff has attempted to homologize the pleurites with those 

 of the other thoracic segments. He describes only three in 

 longitudinal series on each side, which he identifies as the 

 katopleure, anopleure (epimerum), and coxopleure (epister- 

 num). Their relation to the submentum, however, would not 

 bear out this interpretation and the number and position of the 

 plates is so variable that an attempt at their homology appears 

 too conjectural. Apparently embryologists have not attempted 

 to elucidate the subject. 



The thoracic nota or sclerites covering the back of the tho- 

 racic segments are nearly always very complex in the meso- 

 thorax and the metathorax of the adult. But in an orthopteran 

 nymph they are simple undivided plates from the entire lateral 

 margins of which the wings arise. As development proceeds 

 the anterior and the posterior edges become thickened, forming 

 an anterior and a posterior marginal ridge (fig. 7, k and /). 

 From the anterior ridge a phragma may grow downward (figs. 



