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



still fairly numerous, and formed a considerable body of evidence 

 bearing upon the questions alluded to above, and giving distinct 

 answers to all of them, except the one which bears upon the time of 

 life during which the larvae are most susceptible to the influences of 

 the environment, and that which suggests the ocelli as the sensory 

 surface which is influenced. 



Before describing the experiments in detail, I wish to express my 

 sincere thanks to my wife for her kind help in the labour of attending 

 to so many larva?, and in the troublesome work of sewing the leaves 

 together. Mr. Gr. C. Druce has also kindly supplied me with the 

 branches of certain species of food-plant when I was away from home, 

 and has rendered me invaluable assistance in naming the sallows. 

 Mr. J. Gr. Baker, of Kew, also kindly named the Swiss sallows, of 

 which specimens were sent to h'm by Mr. Druce. 



2. Experiments upon the Larvce of Smerinthus ocellatus during 1885. 



The following experiments are arranged in five different series, 

 belonging respectively to five different batches of eggs. There is 

 complete uncertainty as to the male parent (if any) in Series II, and 

 consequently there is some doubt thrown over the male parent in 

 Series III, because in these cases (alone) the same female laid two 

 batches of eggs. The cause of the uncertainty is explained at the 

 beginning of Series II. The series are arranged in a succession 

 which corresponds to an advance in the (presumably) hereditary ten- 

 dency from the whitish towards the yellowish variety. And so also 

 in each series the different sets of experiments are arranged in an 

 order which corresponds to a similar advance in the tendencies known 

 to be produced by the food-plants, i.e., beginning with apple and 

 ending with Salix rubra. 



But the order is merely provisional in the case of less definite 

 tendencies, or of plants which are little known as food-plants. It 

 must also be remembered that the difference between the hereditary 

 tendencies of the various series is very small, because of the failure 

 (except in one case in which very few larva? lived) to obtain any eggs 

 from moths which came from yellowish larva?. 



Series I. 



Eggs were laid in June, 1 885, by a female moth bred from a larva 

 which had been fed during 1884, for the whole period of larval life 

 upon ordinary apple, and which was a typically whitish-green variety 

 (mentioned in "Proe. Roy. Soc," No. 237, 1885, p. 300). The eggs 

 were fertilised by a male moth bred from a larva which had been fed 

 upon crab for the whole of its life, and was a similar whitish variety 

 (also mentioned on p. 300). Hence the inherited tendencies must 

 have been strongly towards the whitest variety of this larva. 



