13. Females of _Pieris Rapæ_, captured in April, laid eggs on
_Sisymbrium Alliaria_. From these caterpillars were obtained, which
pupated on 1st-3rd June. The pupæ were placed on ice from June 3rd till
September 11th (0°-1° R.), and from September 11th till October 3rd in
the hothouse (12°-24° R.), where there emerged:--
On the 23rd of October, 1 female.
” 24th ” 1 female.
” 25th ” 2 males, 1 female.
” 26th ” 1 female.
” 28th ” 1 male, 1 female.
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Total 3 males, 5 females.
All these were sharply impressed with the characters of the winter
form, the females all strongly yellow on the upper side, the males pure
white; on the under side a strong black dusting on the hind wings,
particularly on the discoidal cell. One pupa did not emerge in the
hothouse, but hibernated, and gave in a heated room on January 20th,
1873, a female, also of the winter form.
14. Females of _Pieris Napi_, captured on 27th-28th April, 1872, laid
eggs on _Sisymbrium Alliaria_. The larvæ bred from these pupated on May
28th to June 7th. The pupæ, shortly after transformation, were placed
on ice, where they remained till Sept. 11th (three months). Transferred
to the hothouse on October 3rd, they produced, up to October 20th, 60
butterflies, all with the sharply-defined characters of the winter
form. The remaining pupæ hibernated in a room, and produced:--
On the 28th of April, 3 males, 6 females.
” 4th of May, 1 female.
” 12th ” 4 males.
” 15th ” 1 male, 1 female.
” 16th ” 1 male.
” 18th ” 1 male, 1 female.
” 19th ” 1 female.
” 20th ” 2 males, 1 female.
” 23rd ” 2 males.
” 26th ” 1 male.
” 29th ” 1 female.
” 3rd of June, 3 females.
” 6th ” 1 female.
” 9th ” 1 female.
” 21st ” 1 female.
” 2nd of July, 1 female.
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Total 15 males, 19 females.
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.