LEPIDOPTEROUS PUP^E AND THEIR SURROUNDING SURFACES. 
393 
plant or floor of the cylinders in which the stock was kept. These are useful as 
affording criteria of the normal tendencies of this series. By “ normal ” I mean, in 
such cases, the tendency which manifests itself when the larva is placed among colours 
to the influence of which it is not sensitive; and the resulting pupae deserve the name 
“ normal ” for another reason—because they are generally the commonest forms met 
with. But that they are the commonest merely implies the continual selection of 
certain surroundings which do produce effects on the larva, so that we see that the 
continual repetition of an influence of a certain kind, always, generation after genera¬ 
tion, producing its corresponding effects, may gradually wear out for itself a line of 
least resistance along which the formation of pupal colours will always tend to travel, 
not only when the appropriate stimulus is present, but also in the absence of any 
colour which can act as a stimulus to the larva. Hence, in Mrs. Barber’s paper, we 
learn that by far the commonest forms of the pupa of Papilio nireus are deep green, 
because they nearly always pupate among green leaves, and thus the deep green 
pupae, again and again formed, became the “ normal ” form, or that variety which most 
individuals will assume in the absence of anything which can be a stimulus. Accord¬ 
ingly, we find in Mrs. Barber’s experiments that pale green and yellowish and 
purplish-brown all acted as stimuli and produced pupae of corresponding colours, but 
that scarlet could not act as a stimulus (except to the formation of a small part of 
the colour), and that the resulting pupae were not scarlet, but were of the commonest 
deep green colour. It is interesting to note the completeness of the failure of the 
stimulus in this instance, for the purplish-brown pupae, if produced, would have been 
far less conspicuous on the scarlet cloth than the pupae which were actually produced. 
And similar facts are to be found in these experiments upon V. urticce, when the 
larvae were surrounded by green surfaces, which, in this species, do not act as stimuli. 
Therefore it is of great interest to collect careful notes of the pupae suspended from 
the food-plant, especially when experiments have been made upon others of the same 
series. The pupae of this series were of the following colours :— 
Of the 15 pupae suspended fi’om the food-plant, 5 were . . (4), mostly with normal gold, hut rather 
dull otherwise. 
6 „ light (3). 
4 „ • • (3). 
15 
Of the 5 pupae lying on the white paper floor, on which food and dark excreta 
were also lying ....... .. 1 was . . (4), golden. 
1 „ light (3). 
1 „ . .(3). 
1 ,, dark (3). 
1 „ • -( 2 ). 
MDCOCLXXXVII.—B. 
