80 ANIMAL COLORATION. 



Formerly it was held that A. prorsa, and A. levana were two 

 different though closely allied species : but as long ago as 

 1S30 it was shown that they were merely the spring and 

 summer broods of one species, and produced from identical 

 caterpillars which feed upon the same plant (the nettle). 

 A. lecana is the spring form, A. prorsa the summer form ; 

 the first-mentioned passes the winter in the chrysalis stage. 



Professor Weismann tried by raising the temperature in 

 winter to rear prorsa directly from the offspring of prorsa, and 

 conversely by lowering the temperature in summer to rear 

 levana from the offspring of levana. By lowering the tempera- 

 ture three levana were produced out of twenty, and twelve 

 poritna, an intermediate form, the rest remained prorsa ; by 

 raising the temperature only three out of forty chrysalids 

 produced the form prorsa. Professor Weismann remarks, in 

 his concluding chapter, " that differences of specific value can 

 originate through the direct action of the external conditions 

 of life only," — a conclusion which appears to be justified in 

 spite of the comparative failure to make the influence of 

 artificial warmth felt. Eimer has suggested that it is possibly 

 easier to imitate by artificial means the conditions of winter 

 than those of summer ; and this may account for the failure 

 to convert the winter into the summer form. 



But it should be borne in mind that Professor Weismann's 

 experiments were made upon the chrysalids only, not the 

 caterpillars ; besides, Dorfmeister, who made the same series 

 of experiments, failed just where Weismann succeeded, and 

 succeeded where he failed ; that is to say, he found the 

 influence of warmth more potent than that of cold. 



In spite of the sentence quoted above. Dr. Weismann is 

 inclined to consider the problem of seasonal change more 

 complex. Apropos of some important investigations upon 



