220 Prof. J. O. Westwood on some 



Artliropod than between those organs and the wings, and 

 this, we know, is physiologically the case. Still, however, 

 the instances Avhich I am able to produce in this com- 

 munication prove that the principle of extra development 

 is as applicable to the wings as to the other limbs of 

 insects. 



The first specimen I have to describe is a Gonepteryx 

 Rhamni (PL VI. tig. I), which possesses an extra im- 

 perfectly-developed hind wang. It was taken by Mr. J. 

 Woodgate, of Richmond Road, New Barnet, Herts. 

 Looked at from above, the left hind wing is evidently 

 broader than the right ; in fact, the right-hand true wing 

 is scarcely more than two-thii-ds of the normal size. In 

 fig. la this double right-hand hind wing is represented 

 from above, and in fig. \b, from beneath. From both 

 points of view it is evident that the normal anterior margin 

 of the wing, indicated by the costal vein, a, properly 

 developed, is shown in the supplemental wing in fig. \b, a, 

 whereas in fig. 1 a the costal part of the true wing, with 

 its costal vein, a*, is imperfectly developed ; the postcostal 

 vein, with its two branches, b^ and b", are normally 

 arranged in the true wing, as are also the discoidal vein, c, 

 and the median vein and its three branches, d^, cP and d^. 

 In the supplemental wing (fig. lb) the veins, except the 

 costal one, are more or less abnormal ; the subcostal, b, 

 has only one branch, if we except a very slight indication 

 of bifurcation close to its extremity; the discoidal vein, c, 

 is, in like manner, imperfectly bifurcate at its extremity, 

 which does not reach the outer margin of the wing, and 

 the median vein, d, has only one branch, and is connected 

 with the subcostal vein by two oblique discocellular vein- 

 lets closing the cell, and it is upon these veinlets that the 

 characteristic orange patch, seen both on the normal and 

 supplemental wing, is seen. From this description I 

 think we are warranted in concluding that the true wino; 

 has been sacrificed, and that in the supplemental wing 

 nearly the whole (except the costal portion) has been 

 partially aborted. In the specimen only two legs exist 

 on the side of the monstrous "vvings, but I was not able to 

 examine it sufficiently, for fear of injury, to determine 

 whether a third leg had been broken off. If not, could 

 the extra wing have replaced the wanting leg ? 



The second specimen to be here noticed is a Vanessa 

 UrticcB (PL VI. fig. 2), which was in the collection of the 

 late J. F. Stephens, and of which I published a figure in my 



