392 Mr. F. Merrifield and Mr. E. B. Poulton 07i 



2. Results of the above Experiments. (E. B. P.) 



The pupae of Pieris napi were compared on January 

 2nd, 1899, with a view to the construction of a standard 

 table. 



As compared with the allied P. rcvpiv, the dimorphism of 

 the ground-colour is far more marked. Furthermore, the 

 ground is almost invariably restricted to bone-colour or 

 green in P. napi, whereas many different shades are 

 common in P. rapcV. Even in pupse with the darkest mark- 

 ings the bone-coloured ground is far less obscured by 

 generally distributed pigment in napi than it is in rapfe. 

 There is also in the former a marked dimorphism in the 

 arrangement of the black markings, which show character- 

 istic differences even when present in similar amounts in 

 the two forms — bone-coloured and green. Thus the bone- 

 coloured forms, however pale, almost always possess a 

 distinct black patch (made up of two or three spots or 

 short lines) in the centre of the fore wing. This character, 

 which I call the "wing- mark," is either wanting or far 

 less developed in the green forms, even when more 

 richly pigmented in other parts of the surface. 



Another difference is the far greater irritability of the 

 pupsB of P. napi. A slight stimulus, such as light breath, 

 would almost always cause active movements, when the 

 more stolid pupse of P. rapx remained quiescent. This 

 observation, which certainly held at the time the examin- 

 ation was made, may perhaps have been due to differences 

 in the degree of development then reached by the two 

 species. 



The forms of the two pupse are almost alike, and as each 

 varies considerably, it is very difficult to distinguish them 

 with certainty by this means ; but the above-mentioned 

 tests enabled me easily to pick out two pupse of P. rapse, 

 which had found their place among Mr. Merrifield's numer- 

 ous napi, having been accidentally introduced as larvae in 

 the food-plant. 



The pupa3 of P. napi are either gvc&n or have a hone- 

 coloured ground with black markings and minute dots. The 

 latter may be classified, according to the amount of 

 pigment, as : — 



(1) BarTi, (2) Intermediate, (8) LigJtt. In the light 

 forms the pigment is so small in amount that the pupse 



