64 



white above, and the females with the markings very faintly deve- 

 loped ; but underneath each sex had the nervures strongly edged 

 with dusky scales. Mr. Weir then remarked on the great difficulty 

 there was in generalizing on the subject of the factors in the produc- 

 tion or suppression of markings, and in the intensity of coloration. 



As had been shown, the male of Pieris iiapi had the spring form, 

 with the upper side whiter and the under side darker than the same 

 sex of the later emergence ; then the females of the spring form 

 were certainly lighter above and much darker underneath than those 

 of the summer emergence. The Cavan specimens, coming from a 

 district full of lakes, with a climate not very genial, and the soil 

 mostly "a stiff clay, cold and watery," were quite as distinctly black 

 and white in the later emergence as those of that horaemorphic form 

 in England. 



At the same season of the year, the specimen of bryo7ii(E had been 

 taken, which was not a dusky form of that variety, but having the 

 ground colour quite as yellow as in the type. Then the closely allied 

 Pieris oleracea, from a dreary district on the damp shores of Hudson's 

 Bay, where the snow covered the ground for nearly two-thirds of the 

 year, were remarkable for their whiteness, particularly in the females, 

 which but faintly showed spots. 



The Pieris tnelete found some 15° to 20° further south, both in 

 Japan and China, has the nervures more broadly edged with dusky 

 and the intervening spaces more suffused with dusky scales than the 

 European form, although it is evident from the very large size of the 

 specimen, 2^ inches in expanse, that the climate is a genial one in 

 which it has been developed. 



There is one generalization that has been placed beyond doubt, 

 and that is, that, if the chrysalids, which in the ordinary course would 

 produce the summer form Pieris napi v. napcsce, are subjected to 

 cold, then the result is that the dusky spring form is produced. So 

 long ago as 1873 Dr. August Weismann made the experiment of 

 subjecting numerous specimens of P. tiapi, which should have pro- 

 duced the summer form, for three months to a temperature of 29!° 

 Fahrenheit, and on i ith September placed them in a hot-house, when, 

 between September 26th and October 3rd, 60 butterflies emerged, 

 the whole of which, without exception, and most of them in an 

 unusually strong degree, bore the characters of the spring emergence: 

 the temperature of the hot-house was 59° to 86° F., yet some of the 

 chrysalids hybernated, and produced in the following spring the form 

 characteristic of that season of the year, thus, to put it into Weismann's 

 own words, he "succeeded, with the Pieris, in completely changing 

 every individual of the summer generation into the winter form." * 



One of the most unlooked-for cases of retardation of emergence 

 and change of type is recorded by Weismann. He states that he 



* Those who wish to pursue this interesting subject further will find much in- 

 struction in Professor Meldola's translation of Professor Weismann's " Studies on 

 the Theory of Descent," published by Sampson Low & Co., London, 1882. 



