1904.] PHASES IN BUTTERFLIES. 143 



to have some idea that because a type of pattern and coloration 

 was characteristic of a particular season or climate, it did not 

 necessarily exclude other types : thei-efore that it was not im- 

 possible for phases characteristic both of dry and wet seasons or 

 climates to be sometimes found flying togethei' ; that in a very 

 dry country like Aden it was the rule rather than the exception 

 for wet, intermediate, and dry phases of a species to occur 

 commonly together in each brood. 



That this polymorphic character was probably of earlier date 

 than the more or less defined seasonal phases, of such countries 

 as exhibit great variations of weather at dilferent seasons, seemed 

 evident to me from the fact that in very moist countiies the 

 extreme dry phase of species is exceedingly rare, and probably 

 near to extinction. In Precis sesanius, the dry phase of P. natal- 

 ensis ( = calescens) from Southern and Eastern Africa, the seasonal 

 phases are very distinct, but about equally abundant. In the 

 wet season, as pointed out by me (P. Z. S. 1898, p. 904), both forms 

 may be taken flying together in Mashunaland ; and on that 

 ground I proposed that the term " seasonal form " should be 

 rejected, and the term " seasonal phase " substituted *. On the 

 West Coast P. calescens or natalensis is represented by P. octavia 

 of Cramer and a number of intermediate phases, but no extreme 

 dry phase was recorded until 1901, when, in my " Revision of the 

 Butterflies of the genus Precis " (Ann. & Mag. Nat. Hist. ser. 7, 

 vol. viii. p. 205), I mentioned an imperfect example indis- 

 tinguishable from typical P. sesamus as having been received 

 from Onitsha on the Niger. The extreme rarity of this phase on 

 the West Coast, and the probability that it has become absolutely 

 extinct at Sierra Leone, seem to indicate that it is unsuited to 

 the conditions of a moist climate ; whilst the numerous intergrades 

 from the dry to the wet phase on the same coast certainly indicate 

 the transition from fixed varieties, such as obtain where seasons 

 are well defined, towards a more or less wet type. In Southern 

 and Eastern Africa intergrades between P. sesamus and P. natal- 

 ensis are extremely rare, the most striking of such intergrades 

 being figured by me in 1900 (P. Z. S. pi. Iviii. fig. 1). 



As it is by no means rare for individuals of the wet phase of a 

 species to emerge from the pupa in the dry season, there is no 

 reason why Lepidopterists should be startled when this occurs. 

 They should bear in mind the probability of the fact that, as all 

 the phases of some species occur as simple varieties in extremely 

 dry countries, they also formerly existed as vaiieties in other 

 species ; that the latter, as they gradually extended their range, 

 were subjected to widely difl'erent conditions ; that then the 

 summer phase (as we now understand it) was so conspicuous 

 in the winter, and the winter phase so conspicuous in the summer, 

 that their chance of survival at the unsuitable season was 

 lessened ; and thus it came about in course of time that one 

 variety of the species became the prevalent wet phase, and 

 * See also P. Z. S. 1900, p. 916. 



