396 Mr. 'Ponlton' s fttrtJter experiments upon 



the piippe in Eow III., with the broader Hack hands, were 

 distinctly darker as a whole than those in Rows I. and II. 

 Although no localised effects are produced, the gold and 

 the black certainly influence the pupa, and when the 

 relative extent of one of the areas is increased, its effect, 

 as tested by the whole pupal surface, tends to pre- 

 ponderate over that of the other. 



The bearing of this experiment upon the important 

 physiological questions set forth at the beginning of this 

 section is thus clear, and although nothing new is added 

 to my earlier work, it is at any rate important to confirm 

 by the use of an improved method an experiment upon 

 which conclusions of so much interest depend. 



Mr. Bateson (Trans. Ent. Soc. Lond., 1892, p. 212) 

 states that he glep.ned "no hint at all of the physiology 

 of these phenomena," as indeed was to be expected from 

 the class of my experiments of 1886, which he had 

 selected for repetition. But although he failed to select 

 experiments which would have yielded some information 

 on the point, the experiments had nevertheless been 

 made in 1886, and published with every detail in 1887. 

 Other workers are likely to be discouraged rather than 

 inspired by a statement which, although no doubt true 

 of the writer himself, does not represent the knowledge 

 of the time at which he wrote. For we do possess 

 certain clear indications as to the physiology of these 

 processes, even though they may not carry us very far. 



I now turn to the bearing of the recent conflicting 

 colour experiments upon the smaller points already 

 alluded to (see page 392). 



The larvse, as a rule, tend to mount a vertical sur- 

 face, and suspend themselves from the under side of any 

 ledge projecting from it, but in the absence of the latter 

 they will fix themselves to the vertical surface itself. 

 Advantage of this habit was taken in compelling the 

 larvae to fix themselves to the vertical back of the con- 

 flicting colour case, where the conditions of the experi- 

 ment could be carried out in the best manner. Reference 

 to tig. 5 (Plate XV.) will show the positions selected by 

 many of the larvfe ; for the white bosses of silk from 

 which the puppe were suspended are clearly indicated as 

 white spots in the collotype. It is thus seen that they 

 did not mount to the highest points, but suspended 

 themselves about half-way up or a little above this level ; 

 and this was true of all the rows, irrespective of the 



