LEPIDOPTEROUS PUPAE AND THEIR SURROUNDING SURFACES. 
401 
these experiments have shown, and the uniformity of pupal colour seen in England 
merely follows the uniformity of colour in the surfaces selected for pupation. 
It is probable that this protective resemblance to mineral surfaces is very ancient, 
and it must have been acquired in a dry country, where an exposed rock-surface did 
not weather for a long time ; and it may even date from a period when many of our 
modern aggressive vegetal types had not arisen, and when the predominant green colour 
of the vegetal kingdom contributed less to the total appearance of land-surfaces. And 
the kind of food-plant may have assisted in causing the protective resemblance to 
surrounding rocks, for the common ancestor of all those Pdiopalocera which have gilded 
pupae may have fed on low herbaceous plants, which might have withered in the 
hottest part of the year, and upon which any pupa which protectively resembled 
the green plant would be necessarily conspicuous. Certainly, our three commonest 
Vanessidae pass the pupal stage in the summer, and all feed upon nettle ; but it would 
probably need a far larger amount of knowledge of the life-histories of larvae than we 
possess to make such a comparison as would lead us to conclude as to the exact conditions 
under which this specialised form of coloration originally arose. It is interesting, 
and confirmatory of the above explanation of the biological value of this appearance, 
to consider the way in which certain Yanessidas have adapted themselves to the 
gradual predominance of green in their surroundings. Vanessa lo has a green form 
which, it has been already shown, is commonly produced when pupation takes place 
among the leaves of its food-plant, and the amount of gilding upon this variety is not 
such as would attract attention, for it is not nearly so brilliantly lustrous as that 
described in V. urticce; and, furthermore, the truly gilded form of the healthy pupa has 
probably never been obtained, for no one has yet subjected it to gilt surroundings. 
Hence, when it is said that the green form is more golden than the other variety, it 
is merely compared with the grey pupa produced by dark mineral surroundings, in 
which there is hardly any gilding, or none at all. Vanessa atalanta has no green 
form, and when it pupates on the food-plant it commonly attaches itself to the roof 
of a tent made by the larva, by spinning one or more leaves together. The late 
Mr. Edward Newman describes a most interesting point in this method of conceal¬ 
ment which is often (although I believe not always) adopted. He says (‘ British 
Butterflies,’ 1871, p. 63) : “ When full-fed it constructs a somewhat more elaborate 
retreat ; it gnaws through the petiole of a leaf, or eats the main stalk of the nettle 
within a few inches of the top, not quite separating it; the part thus almost separated 
falls over and completely withers, and this withered portion is formed into a compact 
retreat; from the roof of this the caterpillar suspends itself by the anal claspers, and 
in two days becomes a chrysalis.” This is an exceedingly interesting fact : the pupa 
has no green form, but the larva arranges matters so that the dark pupa shall not be 
surrounded by living green, but by dark withered leaves, and even when it does not 
gain this additional colour-relation it is well concealed in the tent which the larva 
has made. But V. atalanta very commonly pupates on mineral surroundings after 
MDCCCLXXXVII.— B, 3 F 
