EXPERIMENTS IN HYBRIDIZATION AND TEMPERATURE. 289 



It is sufficient for a pupa, of species not only hybernating 

 as imagines, but also as larvae, to be submitted to a temperature 

 of +42° to +45° C for two hours, on two, three, or four con- 

 secutive days, while it is in a sensitive stage, to eventually 

 produce an aberration. 



This will most easily happen in steep mountain slopes or on 

 the face of cliffs, but it might also happen on dark tree trunks, 

 boards, stones, or under leaves, which lie close to a good heat 

 conductor. In breeding, also, puppe which are placed in a green- 

 house or other outhouse, or even in a room, where the sun can 

 reach them, may be subjected to a similar temperature, which 

 is a very natural explanation of the extraordinary aberrations 

 which are bred now and then to the great wonder of the 

 entomologist. 



One point which confirms the validity of this explanation of 

 natural aberrations is, that the aberrations hitherto obtained by 

 the heat experiments all correspond to those found in nature, 

 whereas the aberrations resulting from frost experiments are 

 often forms which have probably never been observed in a 

 state of nature. In order to show the conformity of heat forms 

 with those found on nature, compare the experimentally obtained 

 aberrations figs. 2, 4, 6, 8, with the natural forms 1, 3, 5, 7, 

 which are placed side by side on PI. IV. of ' Experim. zoolog. 

 Studien.' 



The results of these heat experiments * allow the conclusion 

 that the typical aberrations of the nymphalids, that is, about 

 80-90 per cent, of all known aberrations, are brought about in a 

 state of nature by the occasional action of high degrees of heat, 

 +40° to +45°. 



And now for the last question raised by these temperature 



each brood, only normal v. prorsa, L., but later on ab. porima, 0., and very 

 sparingly, several aberrations in very different directions of development 

 (see PI.' II. figs. 13 and 14). The original of fig. 14 is such an extraordinary 

 individual that one does not know at first to what species to relegate it. 

 Each series ended, generally after a pause, in several very large typical 

 levana. A number of pupje stood over and produced in the spring of 1899 

 thoroughly typical V. levana, L. 



The experiments with V. polychloros, L., were not continued in 1898, as 

 a number of fine ab. testudo, Esp., were produced in the heat experiments of 

 1897 {cfr. Exp. zool. Stud. PL IV. figs. 2 and 9). A female of the latter is 

 shown (PL II. fig. 12), as females of this beautiful aberration are very hard 

 to obtain through these experiments in faultless condition and in such ex- 

 treme development can hardly be known in a state of nature. 



'- As the continuance of the heat experiments in 1898 shows (compare 

 the previous footnote), the conclusion arrived at as to the cause of aberrations 

 sensu strictiore in nature of the nymphalids is not only confirmed by further 

 results, but is also shown to be true for a number of Papilionidae and one 

 Lycaenid {Polyommatus amphidamas, Esp.), so that a general agreement 

 seems probable. 



