440 Mr. G. A. K. Marshall on 



iu which the dry and wet phases alternate. Tlie displace- 

 ment of one form of artaxia by another is however no 

 evidence of relative age, but only of relatively better 

 adaptation to the conditions which obtain in the area 

 where the displacement has occurred. Hence the ob- 

 servation recorded by Mr. Marshall seems to me strongly 

 to confirm de Niceville's and Weismann's conclusion that 

 when both seasonal phases exist, both are adaptive. 



Mr. Marshall also shows on pp. 421 to 423 that the 

 species of Precis entirely restricted to forest regions possess 

 cryptic under-sides and habits all the year round, although 

 the dry-season generations are more completely cryptic. 



It is not difficult to understand the observations referred 

 to above, — viz. that the appearance and habits while 

 cryptic all the year round should be more cryptic in the 

 generations of greatest stress. Thus Mr. Marsliall describes 

 the wet-season phase of tlic purple-tipj^ed South African 

 Tcraroli as having under-sides not sj)ccially well adapted 

 for conceahncnt on the <»;round duriiifj tlie resting" attitude, 

 and without the habit of suddenly settling when pursued, 

 modes of concealment adopted by the dry-season generations. 

 In such examples the success of the adaptations may be 

 equal in the two seasons because of the difference in the 

 intensity of the struggle. But tlie extreme seasonal phases 

 of Precis can never be thus understood, because the wet 

 forms are not merely less cryptic than the dry, they have 

 gone over into the opposite camp, and have developed a 

 very extreme, and, except in the examples of mimicry and 

 warning colours, an unknown degree of conspicuousness. 



Another and very interesting form of seasonal dimor- 

 phism is that which has been well known for a long time 

 in the Sati/rin/>\ and consists chiefly in the development 

 of conspicuous ocelli, especially upon the under-side of 

 the wet phases and their greater or less suppression in 

 the dry. No interpretation of the change has, so far as 

 I am aware, been attempted, except that of Portschinski, 

 which has been furtlier alluded to and criticized on p. 398. 

 I thiidv it is probable that a valid interpretation is sug- 

 gested by the result of an experiment made in 1887, and 

 witnessed by Professor Meldola as well as by me. A 

 specimen of Ccenonymiiha j^ainj^Jnlxs was introduced into a 

 lizard's cage. " It was at once obvious that the lizard w^as 

 greatly interested in the large eye-like mark on the under- 

 side of the fore-wing: it examined the mark intently, and 



