913 



INSECTA. 



wings of the segment. This connexion is the 

 great characteristic of the scutum in all insects. 

 The next piece, the sciitellum, (4 c,) is a much 

 broader plate, and is extended across the whole 

 surface of the meta-notum. Like the corre- 

 sponding piece of the meso-notum, it bears on 

 the middle line an excavated shield-shaped 

 plate, and is connected at its external margin 

 with the borders of the wings. The last piece, 

 the post-scuteUum, (4 d,) which, although nar- 

 row like the prascutum, is a strong horny plate 

 that extends on each side, and like the scutel- 

 lum, is connected with the wings. Its posterior 

 margin is bent down to assist in forming the 

 division between the thorax and abdomen, and 

 is connected with the remains of the atrophied 

 fifth segment. The meta-sternum (A) is fre- 

 quently the most developed portion of the 

 meta-thorax, particularly in those insects 

 which, as Audouin has observed, are especially 

 walkers. In Dyticm, the middle piece, the 

 proper sternum (4 g), is a smooth expanded 

 plate, which is produced at its anterior part into 

 a spine, that articulates with the emarginated 

 extremity of the crest of the meso-sternum. On 

 each side of the spine it is developed into a 

 broad, smooth, triangular plate, to the anterior 

 border of which is articulated the episternum, 

 (4_/,) also of a triangular form. This piece oc- 

 cupies the anterior lateral region of the meta- 

 sternum, and the parupteron, (4 e,) which is 

 situated immediately beneath the insertion of 

 the wing, is articulated with its superior border. 

 The epimeron (4 h) of this segment is exceed- 

 ingly small, and appears at first to be removed 

 from its proper situation, being carried upwards 

 to the side of the body by the enormously ex- 

 panded coxa (I). But although removed from 

 its usual situation, and reduced in size, it still 

 retains its characteristic distinction, that of arti- 

 culating with the coxa, and also with the tro- 

 chuntin (?), (k,) which, although minute, is in 

 connexion both with the coxa and epimeron. 

 The meta-furca, or ento-thorax of this segment, 

 (4 s,) is an exceedingly large and important 

 piece, shaped like the letter Y. It is attached 

 at its posterior extremity to a thin vertical 

 plate, which is situated between the united coxae 

 of the legs of this segment, and it is also arti- 

 culated with the posterior part of the internal 

 surface of the meta-sternum. From this at- 

 tachment it is extended upwards and forwards 

 into the middle of the meta-thorax, where it is 

 expanded on each side into two broad curved 

 plates, to which the muscles of the posterior 

 legs are attached. In the middle line it is 

 grooved, and at its anterior part forms a par- 

 tially covered canal, along which the nervous 

 cord is transmitted in its course to the abdo- 

 men. Besides the parts now described, there 

 are also two curved plates reflected inwards 

 from the posterior margin of the meta-sternum, 

 where it is articulated with the coxa;, and also 

 one central vertical one, which arises in the me- 

 dian line from the interior surface of the ster- 

 num, and wlikh appears to be the proper inte- 

 rior sternal ridge. Kach of the posterior coxa; 

 is also furnished with a broad plate, which is 

 situated within the mcta-thorax, on each side of 



the attachment of the post-furca. These parts 

 afford attachments for the muscles of the legs. 



Fig. 387. 



Skeleton of Hydrous picaa. 



A, pectoral surface; B, dorsal surface; 2, pro- 

 notun ; 2 a, prostcrnum ; 2 /, episternum ; mem- 



