SUBSTITUTION OF A WING FOR A LEG IN A MOTH. 71 



developed wing. The absence of a leg in a moth would probably 

 escape observation, and I cannot say whether it has been recorded 

 or not. 



It may be noticed that the normal wing adjacent to the fifth 

 wing in the four other cases of monstrosity that I have mentioned 

 is more or less reduced in size, and, indeed, one would expect that 

 the large abnormal growth would absorb some of the nourishment 

 required for the parts nearest to it, just as one bud on a shoot will 

 sometimes grow at the expense of the rest ; consequently, I should 

 not expect to find in my specimen more than a very small leg, or 

 some deformed object representing one, and I do not think that 

 it is very surprising that there is nothing at all visible, con- 

 sidering that the wing is so accurately placed where the leg should 

 come. It would have been most interesting to have known what 

 the left hind-leg of the larva was like, as I believe that it has been 

 established that there is a connection between the true legs in the 

 larva and the legs in the imago. (Ent. Mon. Mag. xvi., 96.) It 

 is unfortunate that we have only this one specimen to work 

 upon, for though we may no doubt learn much from what is 

 known about the vertebrata, yet one would like to be able to 

 study a few double monsters in the invertebrate kingdom. There 

 are special difficulties in connection with this subject amongst 

 insects, as from their frequent changes of skin in the larva stage 

 and their complicated transformations it is highly improbable 

 that a double monster would accomplish satisfactorily its first 

 change of skin, or, at all events, its change from the larva to 

 the pupa stage. It is, therefore, likely that such cases would 

 be extremely rare in the imago, though they might occur oftener 

 in the young larva, in which they would not have the same 

 chance of being noticed. 



In the present case, whatever represented the extra wing in the 

 larva would be likely to be so small and of such a shape and 

 nature as not to interfere with its successive changes of skin 

 or transformations, so that it would pass through them, as it 

 has done in this instance, successfully, which might not have 



