Experiments upon the colour-relation, dc. 257 
‘possibly this increased length of time may bear upon 
the formation of pigment; or, conversely, that a 
shortened period may be brought about by certain 
reflected colours, and that the absence of pigment may 
ensue as a secondary result. This suggestion,” he 
continues, ‘“‘appears to be worth a careful trial, and, 
even if it does not contribute to the elucidation of this 
most difficult question, the protracted period in darkness 
may be useful to the organism in another way,—to give 
it the opportunity of being affected by surrounding 
colours after change in the conditions of illumination. 
Thus, if the most sensitive part of the period were 
passed during the night, it would be to the advantage of 
the species for such a susceptible condition to be pro- 
longed as far as possible.” In the experiments with 
black Mr. Griffiths adds corroborating testimony to this, 
which he gives in the following words :—“ The length 
of time they were retarded in changing under black 
surroundings was so noticeable as to attract my atten- 
tion, though at the time I did not attach importance 
to it.” 
II. White. 
Although this influence was not made use of in the 
regular single colour experiments of Mr. Griffiths, but 
was used for an attempted production of conflicting 
stimuli, it has already been pointed out that the results 
must be considered here, for the other tints were added 
towards the close of or after the susceptible period. 
The experiments were conducted as follows :—The larve 
were allowed to fasten themselves to the glazed white 
jar, and, as soon as the silken girdle and anal attach- 
ment were completed, a small slip of paper of one 
colour was gently inserted between the points of sus- 
pension, and a second slip of the other colour laid 
under the head and thorax to meet it, thus forming a 
marked opposition of colour influences. In other 
instances the larve were induced to attach themselves 
to tissue-paper, a slip of paper of another colour being 
afterwards inserted beneath the abdominal segments. 
Thus the larve were at no time exposed to the later 
stimuli for more than Stage III., and the susceptible part 
of it must have been entirely excluded in many cases. 
Data. — Four larve, the details respecting which 
