128 WASPS [CH. V 



between the jugum and the overlapping part of the fore- 

 wing. Instances might be multiplied from other orders 

 of insects. 



It is to be noticed that the interlocking of the wasps' 

 wings is effected in such a way as to not only hook them 

 together but also to keep them parallel and in contact 

 during motion. The hooks do not fit into "eyes" but slide 

 upon a bar, and are not disengaged and put out of gear 

 until the wings are brought into the position of rest. 

 Upon the surface of the wings are numbers of short stiff 

 hairs pointing obliquely backward and to the tip of the 

 wing : these catch and get a grip upon the air during the 

 downstroke, but upon the upstroke allow it to slip off. 



The musculature of the thorax 1 (which in this Order in- 

 cludes the first abdominal segment also) is very complicated, 

 inasmuch as this region of the body contains not only all 

 the muscles for the movement of the wings and legs, but 

 also others for the movement of the skeletal parts of the 

 thorax itself. It is to the necessity of affording relatively 

 rigid attachments for all these muscles that the firm, hard 

 exoskeleton of the thorax is due. Passing over the smaller 

 muscles which are concerned with extending the wings for 

 flight or bringing them back into the position of repose 

 and making minor adjustments of parts involved we will 

 attend only to those which bring about the vibration of 

 the wings. Janet 2 has shown that the hind-wings are 

 destitute of muscles and remain motionless except their 



1 Chabrier, " Vol des Insectes," Mem. Mus. 6, 7, 8, 1820. Bennett, 

 Zool. Journ. n. 



3 C. R. Acad. Sci. Paris, cxxvm. 1899. 



