LEPIDOPTEROUS PUP^E AND THEIR SURROUNDING SURFACES. 
3G9 
construction in this place. The bottoms of two flat wooden trays were, in each case, 
covered with black and gilt paper, the different colours meeting along a line which 
ran across the tray, and along which a shelf was fixed covered with gilt paper 
towards the gilt side of the tray, and black towards the black side. The shelves close 
to the tray bottom were perforated with holes separated by equal distances, and the 
size of each hole was such as to easily admit the body of a larva, with its spines, but 
sufficiently small to prevent the occurrence of any considerable space between the edge 
of the aperture and the larval body. In fact, such space as existed was much obscured 
by the larval sjfines. The trays were placed vertically, with the coloured surfaces 
facing a strong east light, and close to the window, so that the shelves projected 
horizontally ; but the black surface was uppermost in one tray, and the gilt surface in 
the other. 
Whenever suspended larvse were found among the food-plant, &c., of the cylinder 
containing the stock they were pinned on to the part of the trays covered with the 
upper colour, in such a position over the holes that the head and thoracic segments, 
and generally the first and second abdominal segments, of each larva passed through a 
hole into the colour beneath, which tended to produce opposite results. This anterior 
part of the body being always strongly curved in Stage III., the head with any 
sensory organs upon it was brought close up to the under-side of the shelf, and thus 
there was no chance of its being influenced in any way by the colour above the shelf 
(which was of considerable depth). Thus rather more than half the total skin area 
was exposed to the upper colour, while rather less than half, together with the head, 
was exposed to the under colour. If the head contained the sensitive surface which 
was being sought for, we should expect that the pupa would be coloured according to 
the influence—already known and gauged—of the lower colour; but if, on the other 
hand, the whole larval surface was susceptible to colour we should expect that the 
results would oscillate sometimes on one side and sometimes on the other, but that, on 
the whole, the preponderance would be in the direction of the tendencies produced by 
the upper colour, inasmuch as there was a rather greater surface of skin above the 
shelf than below it. Beneath the shelf other larvse were fixed upon the lower 
colour only in the case of each frame, in order to form a comparison-experiment. In 
the tabulated account of the experiment, given below, P stands for pupation, and F 
for placing a larva on the frame; while r indicates that pupation took place recently, 
or that the larva was placed on the frame directly after suspension. 
3 R 
MDCCCLXXXVII.—B. 
