THE CANADIAN ENTOMOLOGIST 14 f 



THE PROPLEURA AND 'I HE PRONOTAL SULCI OF THE 



ORIHOPTERA. 



RV E. MELVILLE DUPORTE, MACDONALD COLLEGE (mcGILL UNIVERSITY). 



A l'c\v moiitlis ago while studying the musculature of Gryllus pennsyl- 

 vanicus, I was impressed by the evident homology of the muscles of the meso- 

 and metapleura with those attached to what I then thought was simply an 

 entopleural apodeme of the prothorax. It occurred to me that this process 

 might really represent the propleuron which externally is limited to a small 

 triangular sclerite in front of the coxa. Examination of other Orthoptera 

 convinced mc of the correctness of this view. Recently Crampton* has shown 

 that in Dissosteira Carolina the pleural region is not "crowded out" but overgrown 

 by the pronotum. This is the first published observation on this peculiar con- 

 dition in the Orthoptera, and it has induced me to ccllect and publish my own 

 notes on the subject. 



I was pleased that Dr. Crampton in his paper drew attention to the mis- 

 application of the terms prescutum, scutum, sciiteUum and postscutellum, in re- 

 ference to the areas of the pronotum cut ofT by the sulci. Since it is generally 

 accepted that the sclerites of the meso- and metathorax to which these terms 

 are applied developed as a consequence of the growth of wings on these segments,, 

 and since there is no evidence that the prothorax has ever borne wings it is 

 evident that the pronotal areas cannot be homologous wnth those of the hinder 

 segments. 



I hope to show' that the overgrown pleuron is general throughout the 

 Orthoptera {sens, str.), and that the sulci of the pronotum are integumental 

 folds which originated as the result of mechanical stress. 



a. The Propleuron. 

 The Acridiidce (PI. XII, Figs. 1-3, 12). 



Rhomalea microptera. (Figs. 1 and 2). Externally the episternum is 

 visible as a small, triangular sclerite (Fig. 1, est.) protruding from beneath the 

 anterior half of the ventral edge of the pronotum. The position of the over- 

 grown region of episternum is indicated externally by a darker pigmented and 

 more densely punctate area on the pronotum in front of the third sulcus, and 

 its anterior edge is outlined by a lightly impressed dotted line (Fig. 1). The 

 pronotum can be lifted and cut away from the episternum without difficulty 

 as the two are not very closely united. From within the episternum appears 

 as a triangular sclerite with a convex anterior edge. It extends dorsad nearly 

 half way up the pronotum. Its posterior edge lies against the third sulcus and 

 is infiexed, uniting with the similarly infiexed anterior edge of the epimeron 

 to form the entopleurite (Fig. 2, entp.), a triangular ridge which at its apex near 

 the ventral edge fuses with entosternite or furca. A similar entopleural ridge 

 is formed in the meso- and metathorax of this and other orthopterous insects 

 (cf. Fig. 13, entp. 2). 



The epimeron (Figs. 1 and 2, epm.) is a very narrow sclerite hardly visible 



externally except at its junction with the episternum. Its position, like that 



of the episternum. is indicated externally by a more densely punctate area at 



*Crampton, G. C, The Thoracic Sclerites of the Grasshopper, Dissosteira Carolina, Ann. 

 Ent. Soc. Am., vol. XI, p. .347, Dec, 1918. 

 June, liJlO 



