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



on the normal one. There is very little evidence on which to decide 

 this question, but I incline to the former view, for two reasons, the 

 first of which is the analogous cases in vertebrate animals. With 

 regard to my second reason, it may be noticed in Professor 

 Westwood's two cases of an extra wing that the fifth wing is very 

 abnormal in its veining, some of the veins being absent altogether ; 

 this, together with the fact that the wings proceed from one base, 

 rather suggests the idea of some sort of abnormal growth connected 

 with the wing itself, such as the double legs of vertebrates ; whereas 

 the fifth wing of my Z. filipendulce is almost, if not quite, normal 

 in the veining, and in all respects, except size and colour, like a 

 normal hind-wing of the species. (See plate for neurationof wing.) 

 Size is not an important matter in the wing of an insect, as the 

 wings are very small on emergence from the pupa, and, if inter- 

 fered with at this period, are often arrested in their growth or 

 crippled. Colour depends only on the number and colour of the 

 scales, but the veining is more a matter of structure, and, therefore, 

 much more worthy of consideration. It seems to me, therefore, 

 that as this is a more perfect wing than the supplementary wings 

 in the other cases, and as it is not placed on, or near a normal 

 wing, there is good reason for regarding the moth as a double 

 monster of which only one wing is developed in one individual, 

 the other individual being fully developed with the exception 

 of one hind-leg. 



There is one point in which the present case of monstrosity 

 differs from the case of a hand or arm projecting from a sacral 

 tumour, and that is in the apparently complete absence of the left 

 hind-leg in the moth. I do not myself regard this as a great 

 difficulty, for two reasons. In the first place it is not infrequently 

 the case that a wing is completely absent in a moth, which certainly 

 does not often take place with the leg of an animal. I may 

 mention Macaria notata, in which a hind wing is sometimes absent, 

 and ;v specimen of Dicroramplia simpliciana bred by me lately, in 

 whi.-h the right hind-wing is absent, its place being filled by a 

 very small shapeless lump, which bears no resemblance to an un- 



