1847.] Linnean Society. 349 



fact extremely interesting from the light it throws on the homologies 

 of the nervures and nervules. 



The variation takes place in the genera Ithomia, Mechanitis and 

 Sais, all remarkable also for the great sexual variation in the struc- 

 ture of the anterior legs, those of the males being the least de- 

 veloped, those of the femsdes the most developed, of any butterflies 

 with suspended pupae. 



The state of atrophy of the anterior feet of the males is not, he 

 states, the consequence of excessive development of the other pairs 

 of feet, or of any other organs, nor does it appear to depend on any 

 peculiar habits of the insect ; neither can the greater development 

 of these feet in the females be accounted for by any difference of 

 habits. For the more developed anterior feet of some male Coleo- 

 ptera, for the powerful jaws of the leaf-cutting or timber-boring bees, 

 there are obvious uses ; but a greater development in the one sex of 

 organs almost atrophied in the other, which still leaves them unfitted 

 for the functions they perform in a normal state, and apparently does 

 not render them useful for any other function, can only be explained 

 by conceiving it in some way to depend on the position of the ani- 

 mal in the system of Nature. 



The system of neuration of the posterior wings in the Diurnal 

 Lepidoptera, which may be considered normal as regards this group, 

 is abnormal as it respects the whole order ; and it would seem 

 as though Nature, by a partial return to a normal structure in a 

 few genera, wished to indicate to us the real homologies of these 

 parts. 



In general the posterior wings of the Diurnal Lepidoptera have the 

 discoidal nervure, which in these wings never branches, so placed as 

 to seem to be a third subcostal nervule ; but in some genera, although 

 its basal is always wanting, its real character is very evident, and it 

 is united to the subcostal nervure or one of its nervules, and also to 

 the median nervure or one of its nervxiles, by distinct upper and 

 lower disco-cellular nervules. In the Heliconidte we find this struc- 

 ture, almost normal as it respects the order, in the genus Ituna, and 

 also in Ithomia. It is found in some female Ithomics, of which the 

 males have a different structure, giving indications of that change of 

 position which in the next genus might lead us to mistake the discoi- 

 dal nervure for a fourth median nervule, the disco-cellular nervules 

 being placed more obliquely, the cell becoming thereby more elon- 

 gated, and the lower disco- cellular nervule appearing almost to form 

 a continuation of the median nervure. In Mechanitis both sexes have 



