THE CANADIAN ENTOMOLOGIST. 233 



direction has been taken, it may through the influence of temperature be 

 accelerated or retarded, but cannot be any more changed. It is very 

 possible that a period may be fixed at which warmth or cold might be 

 able to divert the original tendency most easily, and it may exist in the 

 first days of the pupa state. 



If it be asked why in the analogous experiments with napi the 

 reverting was always complete, we may suppose that with this species the 

 summer form has not been so long in existence, and therefore will be 

 more easily abandoned ; or that the difference between the two genera- 

 tions has not become so distinct, which, moreover, indicates that here 

 again the summer form is of younger origin. Or, finally, that the 

 inclination to revert may be quite as great with different species as with 

 different individuals of the same species. But at all events, the facts are 

 confirmed, that all individuals will be moved by cold to a complete 

 reversion. The opinion is expressed in reference to prorsa, that in these 

 experiments it does not depend so particularly on what moment of the 

 development the cold is applied, and that differences in the constitution 

 of individuals are much more the cause why the cold brings these pupae 

 to a complete reversion and those to but a partial one, and has no 

 influence whatever on others. Especially interesting in this relation is 

 the American Papilio ajax. This butterfly, similar to the European 

 podalirius, appears wherever it is found in three varieties, which are 

 designated as var. telamonides, var. Walshii, and var. mar alius. Edwards 

 has proved by experiments, breeding from the egg, that all three forms 

 belong to the same cycle of development ; of such nature, that the first 

 two appear only in spring and always come only from over-wintering 

 pupae, while the last form, var. marcellus, only appears in summer and 

 that in three generations successively. There appears here a seasonal- 

 dimorphism allied to common dimorphism. Winter and summer forms 

 alternate with each other, but the first appears again in two forms, or 

 varieties, telamonidcs and Wahhii. Omitting for the present this com- 

 plication, and looking at these winter forms as one, we have four genera- 

 tions, of which the first possesses the winter form ; the three following, on 

 the contrary, the summer form, marcellus. The peculiarity of the species 

 lies in this, that with all these summer generations only a part of the 

 pupae emerge after a short time (14 days), but another portion remain 

 the whole summer and the following winter in the pupa sleep, in order to 

 emerge only in the spring, and then always in the winter form. For 

 example, of fifty pupae of the second generation which had formed 



