PSYCHE. 



A NEW HYPOTHESIS OF SEASONAL-DIMORPHISM IN 

 LEPIDOPTERA. — I. 



By ALFRED GOI.DSBOROUGH ilAVER, CAMBRIDGE, MASS. 



(/). Previous Researches. 



In 1S30 it was discovered that the 

 two European butterflies Vanessa 

 prorsa and Vanessa, levana were in 

 reality only different broods of one and 

 the same species of insect. The chrysa- 

 lids of the last summer's brood winter 

 over and give rise to butterflies of the 

 light colored, or levana, type. Then 

 follow several summer generations all 

 of the prorsa type, having wings of a 

 dark brown color. The chrysalids from 

 the last prorsa generation winter over 

 and produce levanas the next spring. 

 There is, however, in addition to the 

 forms levana and prorsa, an intermediate 

 form, porima, which is very rarely met 

 with in nature; and, indeed, it was on 

 account of the extreme rarity of this 

 intermediate form that the older natura- 

 lists failed to recognize that levana and 

 prorsa were only different forms of the 

 same butterfly. 



Dorfineister ('64) showed that if 

 chrysalids which were naturally destined 

 to produce the prorsa form be subjected 

 to cold, they will give butterflies which 

 are not prorsa but porima, and that if 

 tlie cold is as intense as o^C. the butter- 



flies which issue are hardly distin- 

 guishable from typical levanas. Later 

 in 1S75 Weismann repeated these experi- 

 ments with the same result. He also 

 tried the reverse experiment. That is, 

 he took chrysalids of the last summer's 

 brood of butterflies and subjected them 

 to the heat of a green house, varying 

 from I5°-3I°C. The chrysalids how- 

 ever remained over winter and pro- 

 duced levanas the next spring just as 

 they normally would had they been 

 exposed to the winter's cold. Weis- 

 mann was deceived by this experiment, 

 and lead into the false conclusion that 

 it was impossible for heat to cause 

 chrysalids destined to produce levanas 

 to give rise to anything but levana. In 

 1S95, however, he published a paper in 

 which he acknowledges that heat can 

 cause the chrysalids which are naturally 

 destined to produce levana to give rise 

 to butterflies of the porima, or even of 

 the prorsa type. His final conclusions 

 ('95 p. 644) are as follows: levana and 

 prorsa follow each other in a regular 

 cycle, levana appears in April, prorsa 

 in June. Bv the influence of cold 

 chrysalids destined to give rise to the 

 prorsa form can be changed into levana. 



