SEASONAL DIMORPHISM OF LEPIDOPTERA. 109 



Seventh experiment loith levana, 1886. — Older larvae, found 

 on Aug. 16fch, were treated as in the fifth and sixth experiments, 

 that is to say, reared in the incubator at 27-31° C. They pupated 

 between Aug. 21st and 23rd. The excessively damp at.nosphere 

 of the incubator, which was not constructed quite suitably, un- 

 fortunately killed all the pupse ; three larvae, however, escaped 

 and pupated in the room, and these produced, from Sept. 6th to 

 10th, three prorsa, with little yellow. 



Digest and conclusion of the levana experiments 5, 6, and 7. — 

 73 prorsa butterflies were bred in consequence of rearing larvae 

 of the third brood in the incubator. In the fifth and sixth 

 experiments the pupae kept alive without emerging. These were 

 kept through the winter at a room temperature of 13-14° C, and 

 produced : — 



On Feb. 9th, 1887, 2 levana males. 

 „ 10th, ,, 1 ,, female. 

 ,, 16th, ,, 1 ,, female. 

 ,, 28th, ,, 3 ,, 

 On March 1st, ,, 1 ,, male. 



8 levana. 



Residts of the levana experiments. — All the experiments 

 newly described here relate to the third brood of the butterfly, i. e. 

 to the brood of the summer generation, or the second brood of 

 the year, which usually hybernates and produces the " winter 

 form" levana in the spring. The species is double-brooded with 

 us, and the larvae of the late summer brood usually forms the 

 first brood of the butterfly of the following year. My experi- 

 ments of the year 1869 have shown that very occasionally in 

 very hot summers this late summer brood of larvae manages to 

 pupate and emerge, and, in Southern Germany, at least, to lay 

 eggs, although it has not been proved by them that these eggs 

 can develop to pupation ; so that a complete third brood can be 

 interpolated in the cycle of the species. 



The experiments then carried out appear to me to prove, 

 that the prorsa-ioxm. can well be changed into the levana-iorm., if 

 the pupae are brought into the cold ; but, on the other hand, that 

 application of heat to the pupae does not succeed in altering the 

 levana brood into the ^rorsa-form. I thereupon concluded, that 

 the levana-ioxva was the older, the prorsa-iorm. the younger. At 

 that time I was working at heredity with conceptions that were 

 not yet very clear, and thought " reversion" to the parent form 

 might, indeed, be possible, but reversion from the parent form to 

 the phyletically younger form is not conceivable. A theory of 

 heredity was then wanting, to which such facts could be referred 

 and subsumed under general propositions. To-day, where I 

 assume difi'erent rudiments to each of the two forms of the 



