306 M ERISTIC VARIATION. [PART I. 



respondent Ix-twccn the segments in the extent to which the spots 

 are developed, though in each case they fade away in the anterior 

 segments (see \\'I.I~M.\N\'S tigs. 59 and 60). 



Another interesting example of considerable uniformity in the 

 colour-variation <>i a series of segments is to be seen in Saturnia 

 earpini. In this species besides change in the tint of the green 

 _'i und-colour [two chief tints being found, one dark and one light] 

 there is immense difference in the amount of black pigment deposited, 

 mo.-t marked in the last two stages of the larvse. Good figures and 

 descriptions of these are given by WEISMANN (PI. vin.). Though no 

 two .segments are alike and though there are differences perceptible 

 even bet ween the two sides of most segments, yet the general scheme 

 of colour of eaeh individual is carried out with fair constancy over 

 the several segments. As I have myself seen, the lightest and darkest 

 may both be reared from one batch of eggs and in the same breeding- 

 cage or slee\ e. 



469. The colour of the tubercles of S. earpini also varies greatly. They 

 may be light yellow, dark yellow, pink, violet, or white, but the yellow 

 and pink forms are the commonest. As I have myself observed, there 

 is generally a close agreement between the different tubercles of each 

 larva in point of colour. In a few specimens I have seen the tubercles 

 of the anterior and posterior segments pinkish, while the remainder 

 wen? yellow, but this diversity is exceptional. The importance of this 

 case is increased by the fact that POULTOX (1887, p. 311) has found 

 that the offsjiriiii: of a pair whose tubercles had been pink shewed a 

 high proportion of larva' with pink tubercles. The two parents were 

 from a lot of 80 larvae found together, of which only 3 had pink tubercles : 

 but of their 88 offspring 64 had pink tubercles. 



470. The case of the occurrence of red spots on the larvag of Smerinthus 

 ocet/dtiix and S. pojmli 1 may be quoted as an instance of great irregu- 

 larity in the degree to which the segments agree in their colour- 

 variations. This well-known case is also of great interest as an 

 example of a parallel variation occurring in different species. The 

 larva 1 of both species are most commonly without any red spots, but 

 not rarely a number of red spots are present. In extreme cases each 

 of the spiracles is surrounded with red, and there is in addition a row 

 of red spots in the sub-dorsal region of all segments from the 1st 

 thoracic to 7th abdominal, and also a red spot on each clasper. The 

 number of spots, number of rows, the size and tint and distinctness of 

 the spots is exceedingly variable. In point of time the spots of the 

 3rd abdominal segment appear first and those of the 2nd thoracic 

 next (POULTOX, 1887, p. 28f>, Arc.). Though in much spotted specimens 

 the spots may remain till the larva is full-fed, in some cases a few 

 spots appeal- at an early stage and are afterwards lost. Among the 

 individuals of the same brood there may be great diversity, some 

 having spots and others being without them (PouLTON, 1887, p. 287). 

 In several cases a spot present on one side of a segment has been 

 found absent on the other side. As Poulton observes, it is especially 



1 I have not referred to the case of S. tilia, as it is possibly of a different 

 nature. 



