XIII 



in colour and form to such climatic influences and of basing thereupon 

 species and subspecies is principally founded on this conception. With a 

 better insight owing to the knowledge acquired concerning the phenomenon 

 of colour evolution I have already in my treatise " Die Farbencvohition {Phy- 

 loorenk del- Farbeii) bei den Pieriden"', published in 1898, pointed out that 

 there can be no ([uestion here of direct special chemicophysical action but 

 merely of a stimulus exercised by the abnormal state of the artificially 

 produced condition in the course of the evolutionary process of change. But 

 this made no impression on the prevalent ignorance and when subsequently 

 Dr. Fischer beean to see that this influence did not act direct but had a 

 retarding effect on the formation of the colours and consequently produced 

 phylogenetically more ancient forms, his want of knowledge regarding the phenome- 

 non of colour evolution confused him sothat he considered both his forms B 

 obtained by moderate heat or cold, and his forms D produced by frost and 

 great heat, as having been caused by retardation whereas a more intimate 

 knowledge of this phenomenon admits only the former as recessive old forms 

 produced by retardation while it indicates the forms D as prospective forms 

 stimulated into development by acceleration. The fact, brought to light by 

 subsequent investigation by Dr. E. Fischer, that the same colour forms may 

 be produced both by heat and cold, completely decided in this matter. For 

 when such abnormal action only produces a disturbance in the course of normal 

 existing processes of nature which, according to circumstances under which it 

 operates, causes retardation or acceleration, the fact that in specific circum- 

 stances it may sometimes produce the one or the other cannot cause surprise. 

 It cannot, however, be reconciled in any way with direct chemico-physical 

 action. Other disturbing influences have gradually been shown to be equally 

 capable of producing the same results. At the International Congress of Zoologists 

 held at Bern in 1904, Dr. M. Countess von Linden stated that by with- 

 holding oxygen during the pupa stage, and doubtless, therefore, by a morbid 

 disturbance, she produced the same changes in the colour of the imagines as 

 had been obtained by Dr. E. Fischer by frost and great heat. My own 

 observations, to be referred to later, concerning the differences in colour and form 

 which occur in the same species of butterflies and have been erroneously termed 

 seasonal varieties, make it extremely probable that the origin of these differences 

 must be sought in the more nourishing nature of the food which the cater- 

 pillars consume during the rainy season which, therefore, also acts as a stimulus 

 promoting the development of such individuals whose susceptibilety enables 

 them to respond to it. Finally, from the pedigree breeding, carried out at 

 Batavia by Mr. Jacobson in connection with an account of Papilio Memnon L., 



