250 Experiments upon the colour-relation, &c. 
whilst blue does not influence the Pieride in any way, 
the pupe being simply normal. 
Before proceeding further it will be well to explain 
what we mean by the term ‘‘ normal”’ in its strict sense. 
Mr. Poulton has applied it to express the results of a 
tendency ‘‘ which manifests itself when the larva is 
placed among colours to the influence of which it is not 
sensitive’; and he further states, ‘‘the resulting pupz 
deserve the name ‘ normal’ for another reason—because 
they are generally the commonest forms met with.” 
The former fact is doubtless explained by the latter, for 
the ‘‘commonest” pupze are those which have been 
most frequently selected as best adapted to the com- 
monest form of surroundings, and this process of 
selection, being repeated generation after generation, 
will gradually form for the larve ‘“‘a line of least 
resistance, along which the 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.’’* 
Preliminary condition of the larve before and after 
capture.—The series of larvee of Pieris rape under con- 
sideration were all, with but one exception, found upon 
mignonette-plants, specially sown by Mr. Griffiths for 
the experiments in his garden. The larve occurred 
upon seven or eight different clusters of plants; and, as 
they varied greatly in size, and in the dates of their 
capture, it is quite clear that we are concerned with 
more than one brood. ‘Thus more than one, and 
probably many, hereditary influences must have been at 
work. ‘The larve were transferred to a breeding-cage 
kept in an outhouse, and were watched daily by Mr. 
Griffiths, being fed upon mignonette up to maturity. 
As they matured and exhibited by their restlessness and 
other premonitory signs that pupation would shortly 
take place,—in other words, whilst they were in the 
transitional period designated by Mr. Poulton *‘ Stage I.” 
of the ‘‘ preparatory period,”t—they were removed 
from the cage, and placed singly, or, in some instances, 
two individuals together (at the most), in separate 
receptacles, generally glazed white jars. ‘The entire 
number of specimens captured was 86; of these 13 died 
* Loc. cit., p. 398. t L. c., pp. 327, 328. 
