The upper ones are the largest, and are continuous anteriorly with the labial glands, the ducts of which open on the mucous membrane of the upper lip.
A long dorsal fln, high and pointed anteriorly, runs along nearly the whole length of the back; the caudal is strong and deeply cleft.
The following is Pettigrew's description of wings and wing movements published in 1867: " The wings of insects and birds are, as a rule, more or less triangular in shape, the base of the triangle being directed towards the body, its sides anteriorly and posteriorly.
The twisting is most marked at the tip and posterior margin, particularly that half of the posterior margin next the tip. The wing when in action may be divided into two portions by a line running diagonally between the tip of the wing anteriorly and the root of the wing posteriorly.
The head is situated on the dorsal side of the body anteriorly within the anterior aperture of the mantle, from which it cannot be protruded.