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Geometrids, which the trained eye can locate in a moment; and one 
hears the remark, “ Those are evidently an Orkney series of Ayrotis 
cursoria,” or “ that is the Shetland form of Cidaria immanata ” ; but 
it is none the less true that both the last-named species vary enormously 
in many of the localities where they occur, and, therefore, they do not 
seem to me to be quite on a footing with Sciadion obscurata. 
That S. obscurata should have acquired a much greater fixity than 
the bulk of the Geometers, which assimilate to much more variable 
surroundings than the bare soil, rocks, etc., to which the first-named 
seems to be entirely restricted, is not difficult to imagine. It is a 
good deal harder to see why so few (if any) of the Noctuids have 
attained to an equally beautiful adjustment, for a great number of 
them admittedly rest on the ground. One can hardly go into the 
numerous probable explanations which arise in one’s mind as one 
contemplates individual cases ; for that would involve the conversion 
of a paper on the variability of one particular species into one on 
variation in general. I will content myself with pointing out that:— 
(1) Some of our Agrotids, etc., are more restricted than D. obscurata 
to some one particular kind of soil, and so have not had the chance of 
exhibiting their adaptability on quite so wide a scale. Take, for 
instance, the sand-hill group, which undoubtedly do vary geographically 
according to the colour of the sand, but do not make such an im¬ 
pression upon us, simply because there is not nearly such a wide 
colour difference between sand and sand, as between black rocks, white 
chalk, and red sandstone, etc. 
(2) The resting posture of our Noctuids is such that they do not 
cover any wide area when seated, and have a much better chance of 
protection than S. obscurata , with its fully-spread wings, even if they 
do not agree with the ’prevailing colour of the soil. There are few 
situations where the conditions of colour are so absolutely uniform as 
to preclude the likelihood of the escape of Noctuid specimens which 
differ therefrom. 
(3) It is possible, also, that the restless Geometrids are more keenly 
persecuted at the time when they should (ideally) be at rest, than are 
the much more lethargic Noctuids, and that they, therefore, stand in 
need of a more absolute protection to counteract this. For instance, 
one may suppose that plenty of Jaspidiaperla on the walls, or Agrotids, 
etc., on the ground, are passed over by their enemies even when only 
very partially protected, provided they remain absolutely immobile ; 
whilst at the same time it might not be within their power to drop 
aud vanish, as most entomologists have seen S. obscurata do at times. 
The last-named is generally such a timid creature that it starts up at 
the very slightest disturbance in its vicinity, half defeating the object 
of its protective coloration ; and if that were not very perfectly adjusted, 
the species would, perhaps, have but a poor chance in the struggle for 
existence. 
On account of the comparative fixity (apparently) of the forms of 
D. obscurata in most districts where it occurs, it would make a very 
interesting subject for experiments in breeding, and I have only been 
deterred from trying it by its unfortunate vice of hibernating as a small 
larva. Perhaps if we raised a large number we should find a larger 
range of variation from a single locality than we at present suspect; for 
it is always possible that reversions to other types, etc., may be taking 
