1903.] R. P. Stebbing — Alar appendages of Chermes abietis-picese. 59 



This is the last stage of development of the insect within the gall, no 

 functional alar appendages being present. 



In opening the upper two edges or sides of the diamond-shaped outer 

 covering of the chamber become detached at their points of juncture with 

 the two lower sides of the cover of the chamber next above, thus form- 

 ing a kind of lip, which can be forced open with forceps. The external 

 surfaces of the diamond-shaped coverings then contract slightly, thus 

 causing the aperture to permanently gape, the opening becoming wider 

 and wider as the surface dries and consequently contracts (fig. /). The slit 

 is at first quite narrow, but as soon as it appears the insects commence to 

 crawl out. On reaching the outside of the false cone the fat purple 

 larva at once undergoes its last moult. In doing this, the skin splits 

 down a median line, both dorsally and ventrally ; as far as the meso- 

 thorax dorsally, and the first or second pair of coxse ventrally ; the insect 

 then slowly crawls out leaving the white papery cast skin, to which 

 are attached the dark-coloured leg and antennal cases, behind it. 



After this last moult it will be seen that the Chermes has undergone 

 a great change. 



It now appears as a small gorgeously -coloured aphid, with black 

 shining head and prothorax, dark orange-brown shining meso- and meta- 

 thorax, both dorsally and ventrally, and with a shining black abdomen. 

 Legs and antenna? bright canary yellow. On either side of the thorax 

 two little bright-coloured bundles are visible, a bright naples yellow an- 

 teriorly and vivid apple-green posteriorly. The whole insect, in fact, is 

 very highly coloured and looks at this stage as if it had just been freshly 

 painted with the very brightest tints in Nature's colour box and then given 

 a coating of varnish. As soon as the Chermes has freed itself from the last 

 attachment of its last skin it begins to crawl actively about on the exterior 

 surface of the gall and the little yellow and green bundles unfold and 

 disclose the fact that they are the rolled-up alar appendages. As far as I 

 could perceive, the insects themselves take no active part in unfolding 

 these wings. They do not hang themselves up to get them unrolled as is 

 the case with Lepidoptera, but simply walk about and under the influence 

 of the sun and heat, the wings rapidly spread out, stiffen, and become 

 functional. I noted that in many cases, even before the insect has entirely 

 freed itself from the last larval skin, the little bundles had so far unrolled 

 as to be quite distinct from one another. Within half an hour from the 

 time of leaving the cone, the wings are fully unrolled, being held at an 

 angle on the side of, but not meeting in a roof-shaped manner over, 

 the abdomen. These wings are pale apple-green in colour with yellow 

 nervures except at their juncture with the thorax where they are chrome- 

 yellow. 



J. ii. 9 



