47 
The question of this variation in the row of spots, how far it is 
vague and accidental, how far it characterises certain geographical races, 
and what are the causes that determine the presence or absence of the 
spots in any particular race, is, of course, intimately associated with 
another point that we are equally ignorant of. That is, what is the 
use of these spots. Whether these problems must be dealt with 
together, or whether one can be first understood and then the other 
more easily investigated, we know not. 
As regards the use of the spots, we may begin its study by pictur¬ 
ing the evolutions of Mr. Trout's tame specimen, which so kindly 
allowed him to observe its persistence in orienting itself in its special 
manner. The butterfly does not so frequently settle on flowers as on 
green leaves, and when it does so moves at once into a position with 
the sun shining vertically on one side ; certainly for basking, but 
whether also for hiding, is not quite clear. It is not very obvious that 
it would be more conspicuous or less so, exposed in this way to the 
sun, than if it sat at any other angle. 
At any rate it is in this position that the row of spots will be most 
obvious, and, therefore, probably that they are then most useful, what¬ 
ever that use may be. The settling amongst leaves certainly points to 
the green colour being for concealment. We must suppose, therefore, 
that the white spots in some way assist this object. It is well known 
that a large area of one colour is more conspicuous than a similar 
surface broken up by varied colours and marking, and the white spots 
will no doubt have some such effect. It seems also possible that they 
may give much the same effect in bright sunshine, as the sparkle and 
shade of the serrated margin of a leaf, such as that of blackthorn, on 
■which the butterfly often settles, the serrations being often convex or 
bent over, and at a different angle to the main surface of the leaf, and 
therefore, when they reflect the sunlight, the general leaf surface will 
not. 
Assuming this to be so, the greater or less development of the 
spots, or rather per contra, their more or less complete obsolescence, 
might be correlated with the plants the butterfly has, in any particular 
locality, as resting places, whether, that is, they have leaves in which 
this effect occurs or not. This is entirely speculative, but suggests 
items for field observations, though perchance such observations have 
already been made by some member of the Society. 
Another peculiarity of T. rubi, in which it is alone amongst British 
butterflies, is the possession of tails, which take a special attitude when 
the insect is at rest. There are many exotic species, of which Mr. 
Kaye, I think, once exhibited a very pronounced example, in which 
these tails take the appearance of an animals head with eyes—to the 
probable discomfiture of enemies. Are these tails in T. rubi merely 
the degenerate remains of the more perfect display that belonged to 
some tropical ancestor, or are they still useful in this or some other 
way ? One would suppose that before such tails could become so 
elaborately mimetic, as in these exotic forms, they must have been 
fairly well-developed, and with some other use. Is T. rubi still at 
this stage of development, and what is the oth^r. use ? 
m 
27 JAH.S13 
XIX. 
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