140 Mr. E. B. Poulton. Colour-relation between the [Feb. 4, 



upon this proof of a larval tendency, than by trusting to the maximum 

 results obtained by the use of food-plants which tend to produce white 

 varieties ; because the power of the latter is so great as to afford no 

 means of discriminating between larvae with different tendencies except 

 when the latter are very exceptionally strong in the direction of yellow. 

 (For the proof of the strong tendencies of the parent larvae, and an 

 account of the effects of various foods upon them, see " Proc. Roy. Soc," 

 as above quoted, pp. 298 — 300.) The larval tendencies in this case were 

 even stronger than in the parents, having been augmented by inheri- 

 tance from the latter. Crab, which has no power in checking the 

 tendency towards white (I cannot yet believe that it causes white itself) 

 produced the most extreme white varieties in these larvae as in their 

 parents (No. 1). But S. rubra (with other similar foods unavoidably 

 used during absence from home) evidently produced less effect than in 

 the case of the parents (No. 4), and the same is true of Salix babylonica 

 (No. 3) if we assume that this plant acts in the same manner as 

 S. rubra. No conclusions can be drawn from the effects of Populus 

 tremula, &c. (No. 2), because this is, I believe, the only instance yet 

 recorded of the larva feeding upon the food-plant in question. 



Series II. 



Eggs were laid by a female moth bred from a larva which had been 

 fed during 1884 for the whole of its life upon Salix viminalis, and 

 which became an intermediate variety with some tendency towards 

 the whitish side. (The larva was one of those mentioned on p. 300 

 of the paper already quoted.) In the case of this moth it seemed 

 likely that no fertile eggs would be laid, for coitus did not take place 

 when I placed a male in the same box with it. After this I put 

 several males in the box, but I did not witness any act of coitus, 

 although I watched the moths constantly, and the act lasts for several 

 hours in all the cases which have come under my notice. In the 

 meanwhile the moth kept laying eggs which I put in a box by them- 

 selves and carefully labelled. The great majority of these eggs 

 shrivelled up, but to my astonishment a few gave rise to larvae which 

 are considered under these series. Subsequently to the laying of these 

 mostly infertile eggs I succeeded in artificially inducing coitus, with 

 the result that a large number of fertile eggs were laid, which were kept 

 separate and are considered under the next series. Inasmuch as many 

 males were present in the box with the female, it would be obviously 

 impossible to maintain that the larvae of this series were partheno- 

 genetically developed, but I may state in favour of such a view that 

 in all other cases the coitus lasted long enough for me to witness it, 

 and that nearly all the eggs behaved like those which were laid by 

 other female moths without coitus. I may add that I always care- 

 fully separated the eggs which were laid before and after coitus, and 



