No, 64 1 DIPTERA OF COXXECTICUT : MORPHOLOGY 51 



meniln-anous suture between this part and the scutelhun, such as one 

 expects to find between true sclerites.'' The occurrence of such a 

 suture between the wing-bearing pLate and the postscutellum of the 

 mesonotum. however, is merely to be expected, since the postscutelhmi 

 arises as a distinct plate of this nature in insects in general, and the 

 Diptera have merely followed the usual plan in preserving such a 

 dividing line between the wing-bearing plate (eunotum) and the 

 postscutellum. as may be seen by comparing the parts (and the mus- 

 cles attached to them) in a series of insects including a plecopteron, 

 a neuropteron of the family Xemoptericlae, a mecopteron such as 

 Bittacus^ and a primitive dipteran such as a tipulid. etc. (See figures 

 by Crampton, 1931.) 



The remarkable similarity between the sclerites of the mesonotum 

 of such Diptera as the Tipulidae and the sclerites of the mesonotum 

 of the mecopteron Bittaciis maj^ be seen by comparing Fig. 6 (of 

 Tlpula) with Fig. 3 (of Blttacus) in Plate 2 of article by Crampton 

 (1919). The character of the sclerites of the mesonotum of the 

 neuropteron Nemoptera (shown in Fig. 5 of the same publication) 

 lends further weight to the evidence from other sources indicating 

 that this neuropteron has retained many features characteristic of 

 the ancestors of the Mecoptera, etc., although Nemoptera itself has 

 developed too many specializations of its own to occupy a position 

 in the direct line of descent of the Mecoptera and Diptera. 



The Mesopleuron. In many Xematocera, the pleural suture, ps 

 of Fig. 6, A and D, dividing the episternal region froin the epimeron, 

 extends as a rather straight line (or one without very sharp curves) 

 from the dorsal articulation of the coxa, ec, to the alifer, or pleural 

 L fulcrum of the wing. The pleural suture, ps^ is not straight in the 

 I mycetophilid shown in Fig. G. B. however, and in the bibionid Aspistes 

 herolinensis (Crampton, 19:25b, PL 6, Fig. '2S) it is markedly bent, and 

 follows a zigzag course as in the higher Diptera, so that the pleural 

 suture is not straight in all of the Xematocera. In the Orthorrhapha 

 Brachycera and the Cyclorrhapha, it becomes increasingly bent, and 

 follows a zigzag course, as is illustrated by the housefly shown in 

 Fig. G, C. in which the pleural suture, /as-, bends sharply forward, and 

 tlien sharply upward, at right angles to its former course, and finally 

 l)ends slightly backward, as it ascends to the alifer. or pleural fulcrum 

 of the wing, just above the sclerit^ labelled sf in Fig. 6, C. 



In the tipulid shown in Fig. 6. A, the episternum is divided by 

 tlie anepisternal suture, as, into an upper and lower region, called 

 tlie anepisternum, aes, and katepisternum, kes; and the epimeral re- 

 Ldon is faintly divided into an upper and lower region, called the 

 anepimeron, aem, and katepimeron, kem, in other insects, although 

 different terms are applied to these sclerites in the Diptera. Thus, 

 < >sten-Sacken (1881) calls the sclerite, aes of Fig. 6, A, the "meso- 

 ; pleura" (a designation which should indicate both flanks or pleura 

 " of the mesothorax), and designates the sclerite kes as the sternopleura, 

 wliile the region aerii is termed the pteropleura. and the composite 

 area composed of the sclerites kem and me^ together with the meta- 



