It should be here mentioned, that similar experiments were made in 1864 by George Dorfmeister, but unfortunately I did not get this information[12] until my own were nearly completed. In these well-conceived, but rather too complicated experiments, the author arrives at the conclusion “that temperature certainly affects the colouring, and through it the marking, of the future butterfly, and chiefly so during pupation.” By lowering the temperature of the air during a portion of the pupal period, the author was enabled to produce single specimens of _Porima_, but most of the butterflies retained the _Prorsa_ form. Dorfmeister employed a temperature a little higher than I did in my first experiments, viz. 10°-11° R., and did not leave the pupæ long exposed, but after 5½-8 days removed them to a higher temperature. It was therefore evident that he produced transition forms in a few instances only, and that he never succeeded in bringing about a complete transformation of the summer into the winter form. In my subsequent experiments I always exposed the pupæ to a temperature of 0°-1° R.; they were placed directly in the refrigerator, and taken out at the end of four weeks. I started with the idea that it was perhaps not so much the reduced temperature as the retardation of development which led to the transformation. But the first experiment had shown that the butterflies emerged between 8° and 10° R., and consequently that the development could not be retarded at this temperature. A very different result was obtained from the experiment made at a lower temperature.[13] Of twenty butterflies, fifteen had become transformed into _Porima_, and of these three appeared very similar to the winter form (_Levana_), differing only in the absence of the narrow blue marginal line, which is seldom absent in the true _Levana_. Five butterflies were uninfluenced by the cold, and remained unchanged, emerging as the ordinary summer form (_Prorsa_). It thus appeared from this experiment, that a large proportion of the butterflies inclined to the _Levana_ form by exposure to a temperature of 0°-1° R. for four weeks, while in a few specimens the transformation into this form was nearly perfect.