534 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



moths, and flies. It may be very gratifying to imagine that it does, 

 but, Avhen it clearly does not, what is gained by imagining that it is 

 as it is not ? 



The i:)ronotiim of nearly all the Orthoptera is a simple plate, but 

 when we come to the Acridiida? we find it divided into four very dis- 

 tinct transverse parts. In fact the pronotum of Melanopliis alTords 

 the most popular illustration of the quadruple construction of the 

 insect back. But here (51) it must be observed that the notum not 

 only covers the dorsum, but has usurped the territory of the pleurites 

 (Eps, FJpm) which it has all but crowded out. An examination of 

 the inner surface (52) shows that the third external groove (s) 

 marks an internal ridge against which the inner lamina of the long 

 posterior reduplication {Rd) ends. The middle groove (//) marks a 

 large internal notal ridge {XR) exactly similar to the internal pleural 

 ridge {PR) of any normal thoracic pleurum such as that of the meso- 

 thorax of Anahrus (44) or of DisHosteira (71). There is present 

 even a notal apodemal arm (A\l) representative of the normal pleu- 

 ral arm {PA). The coxa is carried by an apparently notal coxal 

 process {XCxP) in every way similar to the ordinary pleural coxal 

 process {CocP), though this may really belong to "the rudimentary 

 pleurum. Finally, the leg muscles are disposed upon the notal sur- 

 faces at each side of the middle notal ridge just as they are upon the 

 episternum and epimeruni of a normal pleurum. Hence, it is clear 

 that we have here simply a secondary modification of the notum due 

 to its assumption of the duties of the pleural plates which it has 

 crowded out. It is really most illogical that the pronotum of Melano- 

 pliis should be offered as a typical example of a thoracic tergum, for 

 a tergum doing duty as both notum and i)leura is, on the face of it, 

 not typical. Yet in almost any discussion of insect anatomy the 

 prescutum, scutum, scutellum, and postscutellum will l)e found prin- 

 cipally illustrated by the pronotum of an Acridiid. 



In the Oclonata the pronotum of both nymphal and adult forms is 

 divided into three transverse lobes by two transverse grooves. They 

 are best developed in adults (5, 7, 9, 13), but are well marked also in 

 the nymphs (8, 12). An unusual feature in some is the extension 

 downward from the third lobe of a postepimeral strip {a) of the 

 notum. The meso- and metanotum are sufficiently shown by the illus- 

 tration of Pachydiplax longipenn'is (17). The two are similar and 

 each is subdivided somewhat as in the Acridiida3 and the Perlida\ 

 The wing articulation shows feAV of the characters common to all the 

 other orders except the Ephemerida, and the wing muscles are nearly 

 all attached to the base of the wing itself, a condition peculiar to the 

 order. The pseudonotum {PN) is well developed in each segment. 

 In the mesothorax {PN.,) it is exceptionally large and is divided by 

 ventral ridges into a median and two lateral lobes. 



