1917.] 197 



The inner pupal skin is seen to be less robust ; except on the dorsal 

 ridge, there are no black markings (the black markings on one side in the 

 photograph are due to air-bubblos). It is particularly remarkable that 

 this inner pupa has a cremaster about as efficiently provided with hooks 

 as the outer one. The anal and genital openings or depressions, the 

 suspensory tubercles, etc., are developed much as in an ordinary pupa, but 

 perhaps a little less solidly. The folding in the preparation of the outer 

 skin prevents a detailed comparison, bvit, compared with another pupa, 

 the only difference is the absence of black markings. 



This duplication of the jjupal skin is very difficult to understand. 

 So far as the portion preserved shows, the inner and outer skins fitted to 

 and corresponded to each other exactly, so that one is led to suppose that 

 both were assumed at the same time at the moult to pupa. But other- 

 wise this seems to be a very doubtful hypothesis. How the inner skin 

 could be assumed later, without moulting the outer one, also presents 

 difficulties. Indeed, the difficulty is to form any hypothesis as to how 

 there could be two pupal skins. 



It seems very likely that when the butterfly matured it would have 

 emerged in much the same way as in the case of the ordinary single 

 pupal skin. 



I do not remember to have read or heard of such a case, and as 

 regards my own experience, I have never met with the same condition 

 before, though thousands of pupae and pupa-shells have passed through 

 my hands, and in hundreds of cases with close enough observation to 

 have detected such a condition if present. 



DESCRIPTION OF PLATE IV. 



Fig. 1. — Shows the outer pupal skin of the last five segments of tlie pupa of 

 Fieiis {Mancipium) hrassicae, opened down one side and spread out 

 flat. It resented the flattening sufficiently to become wrinkled 

 down below the spiracles on one side and in the ventral surface of 

 the last segments. The letters d and v mark the dorsal and 

 ventral lines. 



Fig. 2. — Shows the inner pupal skin of the same specimen, reversed in the 

 Plate, to bring the corresponding portions into comparison with 

 fig. 1. It is smaller and less solid and coloured tban fig. 1. The 

 smaller size probably partly due to shrinking in preparation of the 

 softer and more delicate texture, otherwise the two portions are 

 alike. Both are x 10. 



Betula. Reigate. 

 Auff. it/i, 1917. 



