1 6 Experimental Zoology 



required the experimental work of Dorfmeister and of Weis- 

 mann to show that this -supposition was correct. 



Weismann showed for Vanessa levana-prorsa that when a 

 pupa, destined to give rise to the summer form, is kept at a low 

 temperature, it may produce the winter form, V. levana, or a 

 type transitional between the summer and the winter forms. 

 He also succeeded, by raising the temperature, in changing the 

 winter pupa so that it gave rise to the summer type of butterfly. 



More recently Merrifield, Standfuss, Fischer, Grafin von 

 Linden, and others have carried out extensive experiments on 

 the effects of temperature. The butterflies and moths used 

 for this work are usually those having summer and winter broods, 

 that differ in color and often in size, and even in the shape of 

 the wings. In other cases, however, similar changes have been 

 brought about in forms that do not show seasonal dimor- 

 phism. It has been found that not only the summer form can 

 be changed into the winter form, and vice versa, but in certain 

 cases the type may be changed by cold so that it resembles 

 northern varieties of the same species, and by heat to resem- 

 ble southern varieties. Temperatures that are only somewhat 

 higher or lower than normal produce the southern and northern 

 types respectively, while much higher or lower temperatures 

 produce effects that are rarely or never found in nature. These 

 latter changes are sometimes called aberrations. We may first 

 examine a few examples of these effects given by Standfuss. 



The effect of heat on Vanessa cardui is shown in Fig. 5. The 

 colors are much lighter above than those of the normal butterfly. 

 The black bands are much reduced. Similar changes are ob- 

 servable on the under side of the wing. The pupa had been 

 kept for 60 hours at 36-37 C., and then at normal temperatures 

 for six to seven days, when the butterfly emerged. The effect of 

 cold on Vanessa cardui is shown in Fig. 6. The color is darker 

 and the white spots are reddish in tint as seen especially on the 

 under side. The pupae had been kept for 33 days in an ice 

 chest, then for five days in a cellar (+ 13 C.), and lastly for nine 

 days at room temperature. 



