4. From caterpillars of the second generation, found at the same time as those of Exp. 3, 30 pupæ were placed in the refrigerator (temperature 8°-10° R.) on June 25th. When the box was opened on August 3rd, almost all had emerged, many being dead, and all, without exception, were of the intermediate form (_Porima_), although nearer the _Prorsa_ than the _Levana_ type. 5. A large number of caterpillars of the second generation, found at the same time, pupated, and were kept at a high summer temperature. After a pupal period of about 19 days, some 70 butterflies emerged from 28th June to 5th July, all of the _Prorsa_ form, with the exception of 5, which were strongly marked with yellow (_Porima_). 6. The 70 butterflies of the foregoing experiment were placed in an enclosure 6 feet high, and 8 feet long, in which, during warm weather, they freely swarmed on flowers. Copulation was only once observed, and but one female laid eggs on nettle on July 4th. At the high summer temperature prevailing at the time, these eggs produced butterflies after 30-31 days (third generation). All were _Prorsa_, with more or less yellow; among 18 none were completely _Porima_. 7. Young larvæ of the fourth generation, found on the 8th of August, were reared in a hothouse (17°-20° R.). They pupated on 21st-23rd August. Of these:-- A. 56 pupæ were placed on ice (0°-1° R.) for five weeks, and then allowed to hibernate in a room not warmed. In April, 1870, they all gave the _Levana_ form, with the exception of a single _Porima_. B. About an equal number of pupæ were placed in the hothouse, but without any result; for, notwithstanding a temperature of 12°-24° R., not a single butterfly emerged in the course of October and November. The pupæ were then allowed to hibernate in an unheated room, and in April and May gave nothing but _Levana_. 8. Caterpillars of the second generation, found at the beginning of June, 1870, pupated on 13th-15th June, and gave, at the ordinary temperature, on June 29th-30th, 7 butterflies of the _Prorsa_ form. 9. Pupæ of the same (second) generation were placed immediately after pupation on June 18th, 1870, in a refrigerator (0°-1° R.), and after remaining there four weeks (till July 18th) gave, at the ordinary summer temperature:-- On the 22nd of July, 2 _Prorsa_. ” 23rd ” 3 ” ” 24th ” 6 _Porima_, 4 of which were very similar to _Levana_. ” 25th ” 1 _Levana_, without the blue marginal line. ” 26th ” 2 _Levana_, also without the blue marginal line. ” 2nd August, 6 _Porima_. -- Total 20 Of these 20 butterflies only 5 were of the pure _Prorsa_ form. 10. Full grown larvæ of the fourth generation, found on August 20th, 1870, pupated on August 26th to September 5th. The pupæ were divided into three portions:--