INSECTA. 



923 



into a little inflated eminence, which we regard 

 as simply an extended portion of the prsescu- 

 tum unto which the parapteron is attached (3 e). 

 The scutum (3 6) forms a broad convex plate, 

 marked in the middle line by a raphe. It 

 extends from immediately behind the narrow 

 ring of the pronotum on each side to the in- 

 sertion of the anterior pair of wings, and 

 from thence backwards to a point opposite to 

 the margin of the posterior pair, thus forming 

 the greater portion of the proper thorax of the 

 insect. It gives attachment on its internal 

 surface to some of the most powerful muscles 

 of the wings, and consequently requires to be 

 more developed than any other part of the 

 thorax. It is separated by a deep triangular 

 suture from the scutellum of the mesothorax 

 (3 c), which as in Hymenoptera is a large and 

 important part. It forms the lozenge-shaped 

 posterior part of the mesothorax, and if care- 

 fully examined its angles are seen to pass under 

 the sides of the scutum, by the enlargement of 

 which it has been carried backwards. The 

 post-scutellum (3 d} has almost disappeared ; a 

 portion only of it is seen on each side at the 

 base of the anterior pair of wings, bounded by 

 an elevated margin, which extends outwards to 

 join a frcenum that is connected with the 

 posterior margin of the anterior pair of wings. 

 Besides these parts, which form the mesonotum, 

 there are also two broad moveable plates, the 

 paruptera (3 e}, that cover the base of the 

 anterior pair of wings. They are called by 

 Kirby and Spence putagia, or tippets, and are 

 loosely attached by a part of their concave sur- 

 face to the little eminences which we have 

 before noticed at the sides of the praescutum. 

 They are broad arched plates, which in form 

 resemble scapulae, and extend from the anterior 

 part of the scutum, the sides of which they 

 entirely cover as well as the insertion of the 

 first pair of wings. They are always covered 

 with long hairs, and are more developed in 

 Lepidoptera than in any other order. In 

 Coleoptera we saw them placed beneath the 

 wings on the anterior part of the sides of the 

 mesothorax. They were then unimportant 

 organs ; in Hymenoptera they were removed to 

 a position above the wing, but in this order they 

 have arrived at their maximum of development, 

 and appear to be of great importance to the 

 insect. The meso-sternum in Lepidoptera is 

 a part of very difficult examination, and we 

 are not confident that we have rightly made 

 out the analogies of its different parts with 

 those in other insects. The meso-sternum is 

 greatly reduced in size, while the base of each 

 kg is considerably enlarged. It appears to be 

 formed by an union of the trochantinus 

 (fig. 392, 3 A-), and of the coxa (/), these 

 parts in each limb appearing to be united, and 

 distinguished laterally by a very marked suture. 

 The base of the limbs thus occupies the greater 

 part of the meso-sternal region. The part 

 which we thus regard as the trochantinus is 

 articulated in front with the sternum (3 g), and 

 the coxa with the epimeron (3 A). The sternum 

 extends upwards on each side of the segment 



Fig. 392. 



Lateral surface of Sphinx ligustri. 



as far as the upper portion of the epimeron, a 

 little below the insertion of the wings. It is 

 marked transversely by a depression which has 

 the appearance of a suture. At its anterior 

 margin, on the front of the meso-sternum there 

 is a very distinct plate which is united to it by 

 suture, and which appears to be the proper 

 episternal piece (3/). The spiracle or meso- 

 thoracic stigma is situated in a little fossa im- 

 mediately beneath the patagia on each side 

 before the anterior pair of wings, and com- 

 municates with the tracheae between the pro- 

 and meso-thoracic segments. The metathorax, 

 which bears the posterior pair of wings, is con- 

 siderably reduced in size by the developement 

 backwards of the scutellum of the meso-thorax, 

 which encroaches upon this segment poste- 

 riorly, as the scutum anteriorly does upon the 

 prothorax, but not to so great an extent. The 

 preescutum, as in the preceding segment, is 

 concealed within the thorax, being developed 

 inwards to assist with the post-scutellum of the 

 preceding segment in forming the meso- 

 phragma, while only a portion of the scutum is 

 visible on each side of the scutellum of the 

 meso-thorax (4 6), where it forms a triangular 



