192 PROBLEMS OF GENETICS 



the now well-known temperature-aberrations in which the dark 

 pigment is greatly extended. He put together in a breeding-cage 

 2,2 males and io females showing this modification in various 

 degrees. Two of these females died without leaving young. 

 Seven produced exclusively normal offspring. From the eighth 

 female 43 butterflies were bred, and of these there were four (all 

 males) which to a greater or less extent exhibited the aberrational 

 form. 2 The mother of this family was the most abnormal of the 

 10 females originally put in. 



Fischer's experiment with Arctia caja was on similar lines. 

 From pupae which had been frozen almost all the moths which 

 emerged showed aberrational markings. A pair of these mated 

 and produced 173 young which pupated. Those which emerged 

 early were all normal, but of those which emerged late, 17 had 

 in various degrees abnormal markings like those of the parents. 3 

 In neither of these examples is there any question as to the facts. 

 Both observers have great experience and give full details of their 

 work. 



As regards Vanessa urticae, however, it must be recalled that 

 Fischer himself showed that in Nymphalids somewhat similar 

 aberrations could be produced both by heat and by cold, and 

 even by centrifuging the pupae. Frl. von Linden produced a 

 transitional form of the same aberration in V. urticae by the 

 action of carbonic acid gas. 4 It is highly probable that the ap- 

 pearance is due to a morbid change, perhaps an arrest of develop- 

 ment, which may be brought about by a great diversity of causes. 

 In the experiments the cause probably was a diseased condition 

 of the tissues of the mother herself. She had been subjected to 

 freezing sufficiently severe to prevent the proper development of 

 the pigments and some of the ovarian cells presumably suffered 

 also. It will be observed that the only specimens which were 

 affected were the offspring of the most abnormal female, and of 

 them only four out of forty- three showed any change. 



The same interpretation probably applies to the cases in 



2 Standfuss, M., Denks. Schweiz. naturf. Ges., XXXVI, 1898, p. 32. 

 8 Fischer, E., Allg. Ztschr. f. Entomologie, Bd. VI, 1901. 



4 Out of 12 pupae treated 8 died and of the 4 survivors, one only was affected. 

 See M. v. Linden, Archiv. Rassen. u. Gesells., 1904, I. 



