48 
the climate exhibits well-marked wet and dry seasons. Sometimes 
the matter is more complex, for we find that Myoalesis fervida and 
M. surka represent dry-season forms, and M. ustulata and M. oroates, 
the wet-season form of the same species. 
Closely related to this form of variation, are the phenomena described 
by Mr. W. W. Smith, 0 as occurring in Aryyroplvinya antipodum and 
Chrysophan as boldenarum in New Zealand. The fact that the finest and 
best marked, and best developed specimens of A. antipodum are evolved 
in humid seasons, especially if such succeed wet winters, is possibly 
due to atavic causes; since New Zealand, like the British Isles, was 
much wetter at one time than now. The case of the slightly 
ocellated Coenonymplia tiphon, as it occurs on the northern moors of 
the British Isles, and its strongly-ocellated var. philoxenus, occurring 
chiefly on wet, low-lying marshes in the North of England and South 
of Scotland, is worth investigating with precision, as to the com¬ 
parative condition, so far as regards humidity of the atmosphere, in the 
various localities which the species inhabits. This is a matter which 
should not be beyond the power of some intelligent entomologist 
living in our northern counties. 
When I first mooted moisture as a possible and probable factor in 
the determination of melanic forms, the difficulty of how to apply 
moisture tests in a satisfactory manner, so as to produce definite 
results, appeared very considerable. Mr. Merrifield attempted 
some, but the results were negative. This may have been from 
two reasons : (1) The insects selected were not such that moisture 
was a determining character of possible aberration in the particular 
species. (2) The application of the moisture may not have been in 
the particular direction in which it could make itself felt. Seasonally 
dimorphic insects must be, from the very nature of their dimorphism, 
more or less susceptible to differences of temperature. These differences 
of temperature being easily applied to the imago at the actual time of 
its scale formation, the results are marked on the wings in various 
ways. It is clear that seasonally dimorphic forms— i.e., insects with a 
definite winter, and a different summer form, are much more likely 
to be effected then by differences of temperature than by differences 
of moisture, and I should expect that, even where moisture is 
a determining factor in producing aberration, it would be more active 
in the larval than in the pupal state. 
Although Merrifield’s experiments have been without result in this 
direction, the effect of particular experiments by Standfuss are most 
marked. The only explanation probably is, that the examples chosen 
by the latter experimenter lent themselves more readily to treatment, 
and are more readily affected by moisture than the species selected by 
the former. The experiments of Standfuss are described as follows :— 
“ Largo numbers of Satumia pupse kept very dry for 7-10 weeks, from 
June to the end of September, were then freely and repeatedly 
moistened, and about 1 per cent, of the moths emerged from these pupa) 
10-20 days after the damping. The fully-developed moths mostly 
show a departure from the ordinary form of the species, which may be 
characterised as follows : the elements of the pattern are not sharply 
outlined, but more or less washed-out and confused.” Standfuss 
* Melanism and Mclanochroism in British Lepuloptera, pp. 18-19. 
