1887.] beticeen certain Pupa? and their Surroundings, 105 



was a brown variety of the pupa not uncommon in this species. The 

 remaining three larvae were placed in green surroundings, one of 

 them being blinded as above, but only one of the normal larvae 

 pupated, fixed to the green food-plant, and produced a distinct brown 

 variety. These startling results show that there can be no suscepti- 

 bility in this species, and this is all the more remarkable because the 

 two varieties are so well marked, and because of the striking results 

 obtained by Mrs. Barber and other observers on two species of South 

 African Papilios. Fritz Miiller, however, shows that another species 

 of this genus resembles P. machaon in being dimorphic and yet not 

 susceptible. The contradictory results obtained in my experiments 

 were either due to the secondary association of one variety of a 

 dimorphic species with an unhealthy condition or even a stunted size, 

 as the gilded Vanessa pupae result from {i ichneumoned " larvae, 

 or to the shade caused by the green tissue-paper. The eight 

 largest and healthiest larvae produced the green pupae, while of 

 the three smaller larvae only one pupated and formed a brown pupae. 

 Mr. Harwood informs me that he has always looked with suspicion 

 on the brown pupae, believing that they have been bred from larvae 

 which were captured when small, and which are reared in close-fitting 

 tin boxes ; and he believes that the wild pupae, and those obtained 

 from larvae which were found when almost mature, are green. On the 

 whole I think it is probable that the pupal dimorphism in this species 

 is the remnant of a former suceptibility to coloured surroundings. 



Y. Experiments upon Pieris brassicce .and P. rapce. — These two 

 species are treated together because they were in nearly all cases kept 

 under similar conditions and were often placed in the same cylinders. 

 The (nearly mature) larvae were almost always obtained, and the 

 experiments conducted, at Seaview (Isle of Wight). 



1. Standards of Pupal Colour. — Degrees of colour were constructed 

 by the comparison of a large number of individuals in each species. 

 In these standard lists the pupae' were arranged in both species 

 according to the relative predominance of black pigment, both as 

 patches and minute dots, the latter tending to produce a grey appear- 

 ance and obscuring the ground colour. The lightest degrees were 

 classified according to the tint of the ground colour which had become 

 prominent in the comparative absence of the pigment. 



2. Effects of various Colours acting during the Preparatory Period, 

 (a.) Black. — Interesting results following the use of this black ground 

 under various conditions of illumination (P. rapce only), the effects 

 being stronger in the direction of pigment formation when the 

 amount of light was increased (the opposite effect having been 

 witnessed in V. urticce). The pupae of both species were dark in the 

 great majority of instances after exposure to black surrouudings in 

 the larval state during the preparatory period. 



