chap, xi.] WINGS OF INSECTS. 281 



facetted eye. The consistency of the chitinous covering of the 

 head, its sculpture and hairs, colour, &c. are all normal and of the 

 usual structure. The left side of the head however is rather less 

 developed than the right, and the left eye seems to be smaller and 

 somewhat less convex, but there is no special deformity or altera- 

 tion in the facetting. 



At the left side of the head arises an irregular chitinous loop 

 of unequal thickness and having' a diameter of about 2*5 mm. 

 This loop is attached to the substance of the head before and 

 behind and these two attachments are distant from each other 

 about 1 mm. The height of this loop from the surface of the head 

 is about 1 mm. in the highest part. Upon the upper surface of 

 the loop is a small, irregularly rounded eye. The diameter of this 

 eye is about 2 5 mm. and its convexity is considerable. It is 

 facetted, but its facetting is not quite regular and is finer and 

 slighter than that of the normal eyes. VON Kiesen wetter, Bed. 

 Ent. Ztschr., 1873, xvn. p. 435, Plate. 



[A case is recorded by Reitter (Wiener Ent. Ztg., I v., 1885, 

 p. 276) of a Rhyttirhinus deformis, having a "complete and fully 

 formed facetted eye placed on the left side of the thorax." Upon 

 the request of Dr Sharp, this specimen was most kindly forwarded 

 by Dr Reitter for our examination, when it was found that upon 

 the application of a drop of water, the supposed abnormal eye 

 came off. The eye appeared to be that of a fly, and had no doubt 

 become accidentally attached to the beetle either in the collecting- 

 box or before its capture.] 



Wings of Insects. 



Supernumerary parts having the structure of wings have been 

 occasionally recorded in Lepidoptera, but their occurrence is ex- 

 ceedingly rare. In a subsequent chapter detailed evidence will 

 be given respecting supernumerary legs and other of the jointed 

 appendages of Insects and it will be shewn that in very man)' 

 and perhaps all of these cases the supernumerary parts constitute 

 a Secondary Symmetry within themselves (see p. 90). Extra 

 wings however are of a different nature altogether, and there is 

 so far as I am aware no indication that any of their parts are 

 disposed as a Secondary Symmetry. In other words, an extra 

 wing if on the left side is a left wing, and if on the right side 

 a right wing. 



In some cases the extra wing is a close copy of a normal struc- 

 ture, in others it seems to be more or less deformed. No genuine 

 case of an extra wing present on both sides of the body is known 

 to me. 



From the fact that no specimen of supernumerary wing has 

 ever been properly dissected, it is not possible to make any 

 confident statement as to the attachments or morphology of 

 such parts. (See also No. 78.) 



