86 
Several forms of Heterocera mimicking dead leaves in a very per- 
fect way were observed; but there is no reason to enter on de- 
tails about this wellknown sort of protective resemblance. I would 
only venture to say that I had very often the impression that 
several brown coloured butterflies, when flying, resembled fal- 
ling leaves; in fact, I was often uncertain, which I was looking 
on, a brown butterfly or a falling leaf. In any case it seems 10 
me worth while calling attention to this, supposed,, special kind of 
protective resemblance. Piepers (Mimicry, Selektion, Darwinismus. 
1903. p. 232) records similar observations. — But the butterflies 
that caught my special attention were the Lycænids, especially 
the species of the genus Thecla. 
Ås is well known, the species of this genus have some pecu- 
liar, thin prolongations from the hindwings, sometimes only small 
and inconspicuous, but in most species, especially the larger tropi- 
cal forms, long and threadlike. There may be one, two or three 
pairs of such prolongations, of different length, the lower or the 
middle pair being generally much the longest. In most species there 
is a conspicuously coloured spot on the underside of the hindwings 
at the base of the processes; sometimes there are two such spots. 
The upper side of the wings is mostly very inconspicuous and 
quite uniformly coloured, and as the specimens in the collections 
are nearly always mounted with the upper side up, nobody could 
guess the meaning of the tail-like prolongations from an inspection 
of such a collection; from specimens mounted with the underside 
up it can, of course, be concluded with certainty that the much 
brighter colours and often very complicate design of this side of 
the wings must have something to do with the habits of these 
butterflies. But the astonishing truth could, upon the whole, hardly 
be imagined from specimens mounted in the quite unnatural po- 
sition with the wings spread out horizontally, even if the under- 
side be turned up. On observing them in nature, as I had a fine 
opportunity to do during my stay on the island of Taboga, Panama, 
the meaning of the peculiar appendages and the conspicuous design 
of the underside of the hindwings at once becomes evident — it 
is to simulate a false head, so that the butterfly appears to 
be double headed, to have a head in each end. 
These butterflies, when resting, always close their wings, S0 
