15. Several butterflies from Exp. [14], which emerged in May, 1873, were placed in a capacious breeding-house, where they copulated and laid eggs on rape. The caterpillars fed on the living plants in the breeding-house, and after pupation were divided into two portions:—
A. Several pupæ, kept at the ordinary summer temperature, gave butterflies on July 2nd, having the characters of the summer form.
B. The remainder of the pupæ were placed on ice immediately after transformation, and remained over three months in the refrigerator (from July 1st till October 10th). Unfortunately most of them perished through the penetration of moisture into the box. Only 8 survived, 3 of which emerged on the 20th of October as the winter form; the others hibernated in an unheated room, and emerged at the beginning of June, 1874. All 5 were females, and all exhibited the characters of the winter form. Notwithstanding a pupal period of eleven months, they did not possess these characters to a greater extent than usual, and did not, therefore, approximate to the parent-form Bryoniæ.
16. On June 12th, 1871, specimens of Pieris Napi, var. Bryoniæ, were captured on a mountain in the neighbourhood of Oberstorf (Allgäuer Alpen), and placed in a breeding-house, where they flew freely about the flowers; but although copulation did not take place, several females laid eggs on the ordinary garden cabbage. From these caterpillars were hatched, which at all stages of growth were exactly like those of the ordinary form of Napi. They throve well until shortly before pupation, when a fungoid epidemic decimated them, so that from 300 caterpillars only about 40 living pupæ were obtained. These also completely resembled the ordinary form of Napi, and showed the same polymorphism, some being beautifully green, others (the majority) straw yellow, and others yellowish grey. Only one butterfly emerged the same summer, a male, which, by the black dusting of the veins on the margin of the wings (upper side), could be with certainty recognized as var. Bryoniæ. The remaining pupæ hibernated in a heated room, and gave, from the end of January to the beginning of June, 10 males and 5 females, all with the characters of the var. Bryoniæ. They emerged:—
| On the | 22nd | of January, | 1 male. |
| ” | 26th | ” | 1 male. |
| ” | 3rd | of February, | 1 male. |
| ” | 4th | ” | 1 male. |
| ” | 5th | ” | 1 male. |
| ” | 7th | ” | 1 female. |
| ” | 9th | ” | 1 male. |
| ” | 24th | ” | 1 male. |
| ” | 4th | of March, | 1 female. |
| ” | 11th | ” | 1 male, 1 female. |
| ” | 6th | of April, | 1 female. |
| ” | 17th | ” | 1 male. |
| ” | 11th | of May, | 1 female. |
| ” | 3rd | of June, | 1 male. |
We here perceive that the tendency to accelerate development through the action of warmth is, in this case, also very different in different individuals. Of the 16 butterflies only 1 kept to the normal period of development from July 27th to June 3rd, fully ten months; all the others had this period abbreviated, 1 male to eleven days, 8 specimens to six months, 4 to seven months, 2 to eight months, and 1 to nine months.