292 NATURAL SCIENCE, APRIL, 
dark, those of the former species approximating to insects of the 
spring brood, which are normally dark. He has also succeeded in 
producing very dark examples of Lasiocampa quercus, by cooling the 
pupe, and very light specimens of its northern dark variety, callune, 
by heating the pupe (10). In these and other species, there seems 
no reason to doubt that low temperature applied to the pupe does 
induce darkening of the imagine. On the other hand, the upholders 
of the moisture theory deny that there is such a general darkening of 
lepidoptera in arctic latitudes as should exist if low temperature be 
the main cause of melanism, and insist that the climate of the dis- 
tricts where melanism prevails is often mild and equable. This is 
true, but the summer temperature of these regions is lower than that 
of southern England, and much lower than that of Continental 
Europe. It is very possible that moisture may be a true cause of 
darkening; careful experiment might go far to settle the matter. 
It seems clear, however, that moisture or cold, or both, tend to the 
production of melanic varieties, and that these varieties, when pro- 
duced, are specially favoured by natural selection. 
Such observations have been made on few insects except 
Lepidoptera. There are, however, instances of melanism in Coleop- 
tera. My friend, Mr. H. K. Gore Cuthbert, informs me that in 
Irish specimens of the beetles, Badister bipustulatus, Dromius quadvino- 
tatus, Nebria complanata, and Agabus guttatus, the pale spots and 
markings are generally smaller than in English examples. A small 
ground beetle, Calathus melanocephalus, with red pronotum, has, in 
mountainous regions, the pronotum clouded with black (var. nubigena). I 
have lately received this variety (which is considered a rarity in England) 
from the Aran Isles, in Galway Bay, but little above sea level, and 
also from the Faroés. This is a good indication of the similar 
darkening effects produced in mountain, western, and northern regions.? 
Specimens of the common wheel-web spider, Epeiva diademata, 
which I have received from the Aran Isles, also show the same 
darkening tendency. The large conspicuous white spots in form of a 
cross, so characteristic of typical examples of this spider, are reduced 
in these western individuals to small dots. A similar, but less 
marked, variation is to be noted in specimens from co. Donegal. 
Observations on this spider have furnished me also with a few 
facts bearing on the subject discussed in the earlier part of this 
review. The ground colour of the abdomen is well-known to vary 
from light brown through various shades of brown and red to a nearly 
black hue. Among granite rocks I have always found the latter 
variety; as it crouches in its retreat in a crevice of the rock, 
its black and white markings harmonise admirably with the mica 
and white felspar of the granite; but among herbage, the red and 
brown varieties are the morecommon. Whether this correspondence 
1 On the other hand, the black carrion beetle, Si/pha atrata, is represented in 
Ireland by the var. subrotundata, which is generally of a brown colour. 
