FN DEFENSIVE COLORATION 311 



produced angle of the hind wing in certain Satyrine and 

 Nymphaline butterflies are characteristic of the brood of 

 the dry season, when dead leaves are bent and twisted 

 and warped, and that the absence of these characters in 

 the wet season corresponds to a time when such leaves 

 are sodden and lie flat on the ground. Dr. Dixey has 

 shown that analogous seasonal changes occur in certain 

 South American and African Pierinae. 1 In cases where 

 the character and intensity of the struggle for existence 

 vary greatly with the seasons, procryptic defence may be 

 developed in the time of greater stress, the dry season, 

 and very different methods employed by the broods of the 

 other season (see pp. 208-11, 320, 339-41). Seasonal 

 changes of procryptic significance also take place in certain 

 northern species, such as Selenia illunaria, &c. These 

 have been the subject of exhaustive investigation pro- 

 longed over many years by F. Merrifield, who finds that 

 heat applied to the pupal stage is the stimulus under 

 which the changes are set on foot. Much excellent 

 work has also been done on the same subject by 

 Standfuss of Zurich, earlier by Weismann, and first of 

 all by Dorfmeister. 



The laborious experiments of G. A. K. Marshall in 

 South Africa have led to a knowledge of interesting 

 differences in the reactions of different species. Thus, in 

 the Pierine butterflies Teracolus omphale and T. achine, 

 a warm, moist atmosphere applied to the larvae produced 

 wet season butterflies : on the other hand, very little 

 additional effect was produced when the pupae also were 

 similarly treated, and hardly any effect at all when damp 

 heat was applied to the pupae alone. On the other hand, 

 in another Pierine, Belenois severina, damp heat applied 

 during the larval stage produced no result, but when the 

 pupae as well as the larvae were thus treated great 

 effects were manifest. In this species, too, there were 

 interesting differences in the character of the effect, 

 according as heat alone or heat with moisture was applied. 

 It seems quite clear from these experiments that the 

 larva is the sensitive stage in Teracolus and the pupa 

 1 Trans. Ent. Soc., Lond., 1903, p. 157, plate vii. 



