16 INTRODUCTION. 



axillary lobe. Behind this is an indentation of the wing-margin 

 called the axillary incision, and beyond this again (working 

 towards the base of the wing), is a small, more or less well 

 developed continuation of the wing the alula. In some wings, 

 such as those of cuneiform shape, the axillary lobe is, perforce, 

 absent, and the alula is reduced to a minimum. Behind the alula 

 are two more or less rounded, scale-like organs, generally of a 

 dirty white colour, and frequently with a fringe of hairs on the 

 edges ; these are the squamce, and they have given rise to con- 

 siderable dispute as to their correct names. "When the wings are 

 folded, the upper one, which is nearlv always the smaller of the 

 two, partly covers the lower one, and when the wings are out- 

 stretched the upper one moves forward, being actually the 

 extreme base of the wing, and the lower one, then fully disclosed, 

 is seen to be definitely fixed to the thorax. 



The term tegulce appears to date from Loew, in 1844,* when 

 he distinctly differentiated it from the alula (the final basal lobe 

 of the wing), and it is applied to the squama which is fixed to the 

 thorax. Osten Sacken invented antitegula for the anterior scale, 

 to which at times it was necessary to refer specially, and he gives 

 a clear resume of the various terms used for these parts in a short 

 paper.t He also suggests as alternative names to antiteyula and 

 tegula, antisquama and squama, when speaking of each separately, 

 or simply squamae (in the plural), if both pairs together be referred 

 to. In the present work the tw r o pairs, anterior and posterior, 

 taken together are sometimes described as the squama and some- 

 times as the tegulce.+ Since, in the NBMATOCEEA the thoracic 

 quama is very rudimentary, there have been few occasions to 

 refer specially to either the anterior or posterior pair. 



Confusion has frequently arisen owing to many authors calling 

 these structures the alulae ; and a recent writer, Comstock, still 

 adheres to this view, contending that the term tegula should not 

 be employed, having been preoccupied for the cup-like scale above 

 the root of the wings in some Hyinenoptera. A great number of 

 terms have been applied to both the alulae and the squamae, espe- 

 cially the latter, but no advantage would ensue by discussing them 

 here. Yerrall uses the names alar and thoracic squamw, and 

 perhaps these are the most suitable of all. 



As for the halteres or aborted hind wings, they are in some way 

 connected with the power of flight, since if they are removed, a 

 Dipteron flies erratically. They are short cylindrical stems, 

 bearing an oval or flattened knob or club at the tip, and are placed 

 behind and a little below the roots of the wings. The insect can 

 vibrate them with great rapidity in the same manner as a wing. 



* Stettin Ent. Zeit. 1844, p. 326, footnote. 



t Berlin. Ent. Zeit. xli, 1896, p. 285. 



| I am not at all certain that in my earlier writings I have not used the 

 term alula: to designate the tegulce. 



Amongst the terms used for the squamae are calyptrae, alulets, winglets, 

 auricles, ailerons, cuillerons. 



