318 Professor E. B. Poulton on colowr-relation 
it always responds in this way to an environment of the 
kind described above. Bidentata doubtless occupies an 
intermediate position between the other two species in 
this respect. The occasions are probably rare, but not 
altogether wanting, in which it is compelled to develop in 
a green environment. We find that it has the power of 
making some considerable approach towards such surround- 
ings, but not of attaining any high degree of resemblance to 
them. It is probably the case, however, that the tint which 
it produces on green leaves and shoots is of great value 
on a pale yellowish-brown bark, which may often form its 
environment; and it may well be that it is something 
in common between the lhght reflected from this and from 
green leaves which explains the similarity in the effects 
produced upon the larvee 
Typical examples of all the forms of quercifolia larvee 
produced in these experiments were shown alive at the 
meeting of the Entomological Society of London on May 
2nd, 1894, and also at the Soirée of the Royal Society in 
the same month. A brief account of the exhibit is printed 
in the Proc. Ent. Soc. Lond., 1894, p. xvi. Itis also referred 
to in Mr. C. G. Barrett’s “Lepidoptera of the British 
Islands” (Lond., 1896, vol. 101, p. 45). 
The nearly mature larvae of quercifolia, forming the 
subject of the experiments described in this memoir, were 
in almost every case sent to Lord Walsingham, and, with 
the exception of one which was spoilt, were kindly preserved 
by him. The specimens are now to be seen in the Hope 
Department, Oxford University Museum, and in the British 
Museum of Natural History. 
The last series of experiments described in this paper 
grew out of the surprising restriction of susceptibility to 
the younger stages of G. quercifolia. The results naturally 
suggested further experiments upon other species well 
known to be highly sensitive, and I immediately fixed 
upon Amphidasis betularia as the most suitable for the 
purpose. The investigation was carried out entirely by 
the present writer, in the laboratory at Wykeham House, 
Oxford. The results are clearly shown in the accompany- 
ing diagram and summary. ‘he Roman figures represent 
the corr responding stages of larval life. The shaded squares 
indicate stages passed 1 in a black environment, the unshaded, 
stages passed i in the green surroundings. 
