242 



THE ENTOMOLOGIST. 



It must for the present still remain doubtful whether this is 

 actually the ease ; one of my experiments of 1872 contradicts it, 

 since in this experiment pupae of the first brood of the year of 

 P. jiapif which were placed on ice for three months, shortly after 

 pupation produced 60 butterflies with all the characters of the 

 winter form both on the upper and under side, although they 

 had been transferred to a forcing-house on Oct. 3rd, where, in 

 fact, these 60 butterflies emerged up to Oct. 20th. 



One of Merrifield's experiments, on the other hand, is in 

 favour of my view. Pupae of the same second brood of 1892 

 were, as in my experiment, iced from three to four months, and 

 then, when placed in a temperature of 27° C, produced eleven 

 butterflies, which, indeed, exhibited the adaptive green powdering 

 of the under side in the highest degree, but exhibited the charac- 

 teristic features of the winter form less on the upper side, that 

 is to say, those characters which, according to my view, might 

 depend upon the direct influence of temperature. The contra- 

 diction in the results of our experiments on both sides may 

 perhaps be explained by the fact, that in my experiment the 

 temperature of the greenhouse, in which I induced the pupae to 

 emerge, might have been too low (no note was taken of it). 



If we disregard the possibility of the co-operation of direct 

 alterations by temperature, Pieris nnpi behaves just like 

 Vanessa prorsa-levana. In the open only the winter form is 

 seen in the spring, only the summer form in the summer and 

 autumn ; but this alternation of the form does not exactly cor- 

 respond to the alternation of the brood, since generally in both 

 broods a variable percentage does not develope forthwith (" subi- 

 tan"), but remains latent during the following period of flight, 

 and first emerges in the second period following. So far as I 

 know, it has not been ascertained by experiment how large this 

 percentage is, nor within what limits it fluctuates ; I see, how- 

 ever, from a remark of Merrifield, that sometimes half of the 

 first brood of the year do not emerge in the summer, but first 

 emerge in the next spring, and in one of my old experiments 

 with napiy in which all the individuals of a large brood of the 

 summer generation did not emerge in the summer, but first 

 emerged in the next spring, it has been quite rightly interpreted 

 by Merrifield as a *' congenital tendency" to hereditary hyberna- 

 tion. It happens from this, that, under circumstances, an entire 

 brood can remain latent the following period of flight. Influenced 

 by the thought that the direction of the development is largely 

 determined by external influences, I had then sought for such an 

 influence as the cause of the phenomenon, and I believed that I 

 could find no other for this, as I believed, quite exceptional be- 

 haviour, than the mechanical shaking, to which the pupae were 

 subjected during a seven hours' railway journey. In the mean- 

 time Merrifield, not, indeed, with napi, but with other double- 



