198 Dr. F. A. Dixey on 



former, however, says Butler, is a fact that can be proved 

 from the data on the Museum specimens.* 



Statements of this kind, the list of which could be largely 

 extended, go far to show that the case of Catopsilia pomona 

 and C.crocale is by no means an isolated one, and that just 

 as there are regions in which more than one geographical 

 form of a widely-ranging species may be found flying 

 together,^ so there are districts of a greater or smaller 

 extent where diverse forms of a species, confined for part of 

 its range to definite seasons, may all occur simultaneously. 

 No doubt the data are as yet insufficient for a complete 

 explanation of these phenomena. It seems, however, clear 

 that the forms or phases which are usually called " seasonal" 

 may occur under many diverse conditions and in many 

 different proportions. It appears further that they do 

 not fall into a regular system of succession, except in the 

 presence of regular alternations of season, and not always 

 then. I still venture to think that a probable view con- 

 cerning many of them is that briefly expressed by me 

 some years ago in " Nature " (Vol. Ix ; 1899, p. 98), viz., 

 that polymorphism, however it may have arisen, is capable 

 of being brought more or less into relation with locality 

 and season under the influence of natural selection. On 

 the other hand, it is conceivable that in some cases at all 

 events the forms in question may have first arisen as 

 adaptations to the seasonal changes, and aftervvards, in 

 consequence of extending their range, or of some other 

 alteration of conditions, may have partly or entirely lost 



* Ann. Mag. Nat. Hist.., 1897, ii, p. 386 ; Bnd., 1896, ii, p. 335. The 

 following instances may lie added from specimens with data in the 

 Hope collection : — (1) Australian form of Terias hecabe, Linn. {T. 

 suljiliiirata, Butl.) ; the diy, wet, and intermediate seasonal forms, all 

 taken liy Mr. J. .J. Walker, R.N., on June 19, 1890, at Port Darwin, 

 North Australia. (2) Teracolns phlegi/as, Butl. (T. difficilig, E. M. 

 Sharpe) ; a wet-season male taken paired with a dry-season female, 

 both in good order, l)y Mr. G. A. K. Marshall, May 3, 1899, at 

 Salisbury, Mashonalaud. (3) Teraeolns vestalis, Butl. ; the wet and 

 dry-season forms both taken at Karachi on May 10, 1888, by Mr. 

 W. D. Cumming. (4) Belcnois severina, Cram. ; wet and dry-season 

 forms Ijoth taken on Feb. 13, 1897, at Karkloof, Natal ; a wet-season 

 male paired with a wet-season female, and another wet-season male 

 with a dry-season female on Feb. 24, 1897, at Malvern, Natal. All 

 these by Mr. G. A. K. Marshall. 



f E. g. the various forms of L. chri/sijypvs, Linn., wliich are all 

 found together at Aden. See Butler in Proc. Zool. Soc, 1884, pp. 

 478-481 ; aud Col. Yerbury in Journ. Bombay Nat. Hist. Soc, 1892, 

 p. 209. 



