19 



We may, therefore, conclude that in P. napi also the period of emerg- 

 ence is determined before pupation. Some experiments were carried 

 out by Weismann in 1873. I have not been able to refer to his original 

 account of them, but, from Mr. Jenner Weir's note in our " Pro- 

 ceedings" for 1892, I gather that numerous specimens (I fancy he 

 means pupae) which should have produced the summer form were 

 subjected for three months to a temperature of 30 F., and on 

 September nth were placed in a hothouse with a temperature 

 ranging from 59 to 86° F. Between September 26th and October 

 3rd sixty butterflies emerged, all of which in a strong degree bore 

 the characters of the spring emergence ; some of the pupae did not 

 then emerge, but produced in the spring the form characteristic of 

 that season of the year. As Weismann says, he " succeeded in 

 completely changing every individual of the summer generation into 

 the winter form." 



However, with the limited knowledge I have of the experiment, it 

 seems to me he was unable to change the predetermined period of 

 emergence, those which intended lying over till the spring doing so 

 in spite of the temperature conditions. 



From the experience of Mr. Harrison and myself, we find that 

 P. napi, in addition to the seasonal forms, has a decided tendency 

 to produce "local' forms." Speaking generally, the Irish and 

 Scottish specimens are darker than English specimens of the corre- 

 sponding periods. We find also that Manx and Cornish specimens, 

 when examined in long series, differ materially from series from 

 Cheshire and various places in the south of England. Again, those 

 of the summer emergence are, as a rule, larger insects than those 

 of the spring emergence. Another point, to which I have already 

 referred, is that the spring emergence consists partly of the progeny 

 of the butterflies of the previous spring and partly of those of the 

 summer. I have not sufficient data to be able to say whether these 

 two broods are identical, or in any way distinguishable one from 

 another, and think information is wanted concerning this. 



I am afraid that, in opening this discussion, I have undertaken a 

 task for which I am not well prepared, and must confess my igno- 

 rance of the experimental work of Weismann, Merrifield, and Prof. 

 Bateson. My shortcomings will give a good opportunity for others 

 during the discussion. My experience refers chiefly to the seasonal 

 and local forms we have obtained by breeding series from various 

 places in the British Islands and from the Alps, some of which Mr. 

 Harrison will exhibit. 



