126 TEXT-BOOK OF ENTOMOLOGY 



the disarticulation of the elytra, but Hoffbauer thinks that they serve as con- 

 trivances to retain the air which the beetle carries down with it under the sur- 

 face, since he almost always found a bubble of air concealed under it ; besides, 

 their folded and fringed edge seems especially fitted for taking in and retaining 

 air. Hoffbauer then describes the teguhe of the hornet and limls them to be, 

 imt as Cholodkovsky states, hard, solid, chitinous plates, but hollow. They are 

 inserted immediately over the base or insertion of the fore wings, being articu- 

 lated by a hinge-joint, the upper lamella extending into a cavity of the side of 

 the mesothorax, and connected by a hinge-like, articulating membrane with the 

 lower projection of the bag or cavity. The lower lamella becomes thinner 

 towards the place of insertion, is slightly folded, and merges without any art iou- 

 lation into the thin, thoracic wall at a point situated over the insertion of the 

 fore wing. The teguhe also differ from the wings in having no muscles to move 

 them, the actual movements being of a passive nature, and due to the upward 

 and downward strokes of the wings. 



Comstock adopts Meinert's view that the elytra are not true fore wings, but 

 gives no reasons. (Manual, p. 495.) 



Dr. Sharp, 1 however, after examining Dyticus and Cybister, affirms that this 

 structure is only a part of the elytron, to which it is extensively attached, and 

 that it corresponds with the angle at the base of the wing seen in so many 

 insects that fold their front wings against the body. He does not think that 

 the alula affords any support to the view that the elytra of beetles correspond 

 with the tegulse of Hyrnenoptera rather than with the fore wings. 



That the elytra are modified paraptera (tegulse) is negatived by the fact that 

 the latter have no muscles, and that the elytra contain tracheae whose irregular 

 arrangement may be part of the modified degenerate structure of the elytra. 

 Kolbe finds evidences of veins. The question may also be settled by an ex- 

 amination of the structure of the pupal wings. A study of a series of sections 

 of both pairs of wings of the pupa of Doryphora and of a Clytus convinces us 

 that the elytra are the homologues of the fore wings of other insects. 



e. Development and mode of origin of the -wings 



Embryonic development of the wings. The wings of insects are 

 essentially simple dorsal outgrowths of the integument, being evagi- 

 nations of the hypodermis. They begin to form in the embryo before 

 hatching, first appearing as folds, buds, or evaginations, of the hypo- 

 dermis, which lie in pouches, called peripodal cavities. They are 

 not visible externally until rather late in larval life, after the insect, 

 such as a grasshopper, has moulted twice or more times; while in 

 holometabolous insects they are not seen externally until the pupa 

 state is attained. 



The subject of their origin is in a less satisfactory state than de- 

 sirable from the fact that at the outset the development of the wings 

 of the most generalized insects, such as Orthoptera, Termes, etc., 

 was not first examined, that of the most highly modified of any 

 insects, i.e. the Muscidae, having actually been first studied. 



1 Proc. Ent. Soc. London. Feb. 19, 1896. Heymons also shows that the germs of 

 the elytra of the larva of Tenebrio molitor in the prepupal stage are like those of 

 other insects. (Sitzungs-Ber. Gesell. natur f. Freunde zu Berlin, 189(5, pp. 142-144.) 



