X. 
Why Ireland and the Isle of Man are so sunless, I do not know. I 
have tried to think that the action of the Gulf Stream might produce 
such results, but Mr. Barrett’s account of the pure blue sky and 
perfectly clear atmosphere at Pembroke, shows that it is not so. 
Besides, the effects of the Gulf Stream are not confined to the narrow 
limits given by Mr. Tutt, they extend over all our western and 
southern shores, and even to the coast of France. I leave the 
explanation for the meteorologists of Ireland. The facts we know 
are that the skies are comparatively sunless, and that melanism is a 
marked characteristic of the Lepidoptera. 
In the manufacturing districts of the North of England the 
appearance of melanic forms there, exactly coincides with the great 
increase of factories, chemical works, blast furnaces, and such like 
smoke and fume producing places, which have been est- blished during 
the last half century, and, as they have increased in number, so have 
two facts in connection with Lepidcptera become apparent. First, 
the more delicate species have become extinct, and Second, the more 
susceptible have become melanic. There is considerable difference to 
be observed in the susceptibilhy of different species. The first noticed 
in this country was Amphydasis betularia , and singularly enough, it has 
apparently been the first species to become melanic in the manufactur¬ 
ing districts of Germany. Red, green, and black, are the most 
heat-absorbing colours, and Lord Walsingham has proved that in 
black this applies to insects, and he has also shown that it is probably 
so with red. With reference to green it is somewhat singular that in 
my district Polia chi has become green under the clouds of smoke, 
whilst in the Yorkshire districts it tends towards black. Enpithecia 
rectangulata which is normally green, has under these smoky clouds of 
both London and Newcastle become quite black. There are many other 
apparent anomalies, thus, Irish male Mendica are not black, but nearly 
white, and the genus Fidonia is found to have a whiter gromea colour 
in the North and a yellower in the South, and with the closely allied 
Strenia clathmta the same rule obtains. But no doubt all these 
apparent difficulties will be explained in due time ; the chemistry of 
insect colours has scarcely been studied at all. At present we 
may confidently assert that whatever impedes the direct rays of the 
sun, has a tendency to create melanic forms in Lepidoptera. 
