GRADUAL FORMATION OF PIGI^IEXT ON PUPA OF PAPILIO MACHAON. 2G3 



seated source. About 10.0 the middle portion of the median nervure 

 of the wing, with the three principal nervures branching from it, and, 

 soon after, the subcostal nervure and its fork, began to show them- 

 selves as of a darker green than the rest of the wing ; soon afterwards 

 the head and coverings of the eyes, mouth-parts, antennjp, and legs 

 began to darken ; also parts — chiefly the rough prominences on the 

 back — ^of the thorax. By 11.0 dark pigment commenced to appear in 

 these thoracic dorsal regions and on the nervures and nervules above 

 referred to, also about the head, especially on its dorsal aspect. At this 

 time the ground colour of the pupa in the parts not darkened had 

 become dull yellowish bone colour on the abdomen and back of the 

 thorax, greenish dusk on the wing cases and on all the rest of the 

 pupa. By 1.0 p.m. the dark parts had become much darker, but the 

 light parts still preserved a slight greenish tinge. By 7.30 p.m. the 

 dark parts had spread considerably, so that much the greater part of 

 the pupa had become suffused, including the head, all the limbs, the 

 whole of the wings except a central portion not representing more than 

 half the area of the forewing, except also the ventral portion of the 

 abdominal region, and a broad longitudinal band on each side of the 

 dark subdorsal bands, which had now almost united into one, these 

 lighter bands being continued, in a somewhat darkened hue, along the 

 thorax ; all the light parts were more or less darkened, and had lost 

 every trace of the greenish. The dark parts had become much more 

 intense in hue, the head especially and the anterior portions of its 

 appendages and those of the thorax being blackish, shining where 

 the light fell, so as to give them in parts almost the appearance of 

 having been plastered with tar. 



About 2.25 p.m. I observed another pupating larva, of which the 

 larval skin had just begun to split over the thorax. I watched it until 

 the whole of the larval skin had been cast off, and noticed that all the 

 parts which were dark in the pupa first described at 8.30, were dark at 

 the moment of their first appearance through the split skin. This 

 second pupa had small blackish spots in the subdorsal region, not only 

 on the 1st and 2nd abdominal segments, but on most of the others. 

 By 4.0 p.m. there was still no darkening except on the abdomen. By 

 7.0 p.m., when I again examined it, the nervures of the wings had 

 become blackish and the head had darkened. By the next morning 

 the pupa had attained its full darkness, or nearly so, very nearly 

 resembling the first pupa. 



I watched several other dark pupsp in different stages after the 

 casting of the larval skin, but was not able to do so continuously, 

 sufficiently, however, to show that the detailed description above given 

 is of general application. 



It would appear from the foregoing observations that when a pupa 

 of P. marhaon is going to be dark coloured (a destination fixed in the 

 period of larval existence when feeding has ceased, as so fully investi- 

 gated and ascertained by Professor Poulton) very small portions are 

 darkened while the pupa is still clothed with the larval skin ; that 

 after this there is very little change in colour for nearly two hours, and 

 that afterwards the abdomen colours before the anterior part of the 

 pupa. It should be understood that the temperature during the whole 

 period of observation ranged from about GO"^" to G4° ; one of 80'^ would 

 doubtless have much accelerated the changes. I have alwavs found it 



