32 
(if this be true) and may safely be perpetuated and increased by 
increase of vigour especially by protected $ s. (The confluence of red 
spots in Zyyaenidx may be asthenic variation). 
This explanation of $ colour consorts much better than mere 
display with undoubted facts. Thus, in Aylaia, instead of sexual 
selection by colour, would be predominance of brighter $ s, per greater 
vigour. $ Aylaias devoid of chaste outline and golden beauty, and all 
that makes the wings of one better than another, devoid of this to a 
greater or less extent, can be seen to prevail against $ s of tenderer 
age, and certainly fairer form, in pairing. And this does not go on all 
fours with evolution of bright colours in $ , by choice by £ of colours 
per se. 
This has been watched not once nor twice, but many times. 
Then accept that:— 
i. Superaestival seasons (within reasonable bounds of supersestivity) 
are associated with some increase of vigour. 
ii. With increase of vigour some intensification of sexual character¬ 
istics is liable to be associated. 
iii. Prevailing $ s in cases of competition are liable to be those of 
increased vigour, and intensified characteristics, 
and we have a chain of theories so superficially simple and so agree¬ 
able inter se, that one feels sure that there must be much to be urged 
against them. 
One cannot, one knows, be justified in regarding so simply as one 
has, for brevity, treated it, the subject of this discussion, but one 
ventures to express a hope that sufficient possible evidence has been 
suggested to give another motive for, an increased pleasure from, study 
of at least some lepidoptera on newish lines ; at any rate, a hope that 
possible evidence offered seems sufficient to make it seem worth while 
to look out for evidence for and against the theory, which will be some¬ 
thing more than the amusement of being invited almost in the same 
breath, to consider a number of poorly marked aberrations as possibly 
of greatly more importance than a few extremes, and immediately 
after invited to be content with a very small show of specimens. 
It may, however, well be (as one would be inclined to predict) that 
rarer extremes of departures in sexual dimorphism from average, e.y., 
Corydonius in Corydon, Alpina in Astrarche, etc., coincide with periods 
of abundant, slighter examples showing tendency to the same. 
Even so their value as evidence in support of these ideas is possibly 
of no more importance than, as an objection is the persistence of the 
opposite, viz., that individuals which remain almost, or quite resistant 
to the abnormal conditions, still occur in the most unusual seasons. 
When we take all these considerations together with the reflection 
that it would probably be true to say that in every year extensive daily 
collecting over a wide area would probably furnish examples of all but 
extreme aberrations, in greater or less degrees, all these considerations 
point to large fields for work opened up by the adoption of the hypo¬ 
thesis, that “ when sexual dimorphism is affected by weather, sub¬ 
normal conditions are associated with tendency to decrease the sexual 
dimorphism, and vice versa.” 
Undoubtedly, for the meagre and inconclusive gleanings from these 
fields, and the incomplete array of specimens such as might tend to 
prove the hypothesis, every apology is due, and freely offered. 
xviii. 
