PLEBETUS ARGUS. 217 



obsolete ordinary hairs, as such hairs as the special filamentous one. 

 One point that comes out is that the hairs, etc., have moved back- 

 wards, or, otherwise expressed, the chitinisation forming- the plate has 

 moved forward. The posterior hairs have moved backwards off the 

 plate, the lenticle has moved from the front margin to the middle. 

 In another specimen, one side has a lenticle close to the special hair, 

 and another just in" front of the middle, the other side has none ; each 

 side has three symmetrical hairs, and one or two not represented on 

 the other side ; this plate is more fully armed than the one noted 

 above. Another specimen has a large lenticle and two long hairs 

 (longest, however, about O05mm. only) symmetrically placed on each 

 side, and several obsolete hair-bases irregularly placed; the hair dis- 

 placed backwards is duplicated on one side. It would be tedious to 

 describe several other specimens, but no two are alike. It is obvious, 

 however, that no detailed description of the disposition of the hairs 

 at this or later stages can have much, if any, value for defining 

 specific characters. On the remainder of the prothorax are, on each 

 side, some 35 hairs, and one or two lenticles. On the mesothorax, in 

 the specimen selected for description, there is a dorsal azygos lenticle, 

 the dorsal hairs on i and ii doubled as in the first instar (antea, p. 215) 

 with lenticles, and, in addition, eight or nine hairs down to the region 

 of iii ; the flange hairs are six, the marginal five and a lenticle. The 

 mesothorax has the setae of i and ii both large, with two or three smaller 

 hairs, and two large lenticles ; the spiracle has, immediately above it, two 

 large lenticles and a long hair (0-2mm.), and a small club-shaped one ; 

 the flange-haii s four in number, the marginal three and a lenticle. The 

 2nd abdominal has precisely, as in the first instar, three dorsal hairs 

 and two lenticles, but, instead of the two minute hairs on iii, it has, 

 like the 1st abdominal segment, a long hair (iii) above the spiracle 

 and a short one and two lenticles; on the flange four hairs, and three 

 marginal hairs and a lenticle. On the 3rd, 4th, 5th, and 6th abdominal 

 segments, tubercle iii no longer has a long hair, but, as in the first 

 stage, carries two clubbed hairs, proportionately larger, together with 

 two lenticles. On the 7th abdominal segment, that on iii is much 

 the longest hair on the segment, and immediately above the spiracle ; 

 it is about 02mm. long, its base and basal half are like an ordinary 

 hair ; its terminal half is, however, swollen, so as to make it a very 

 large specimen of a clubbed hair ; the other hairs on this segment are 

 small ; the dorsum has the slit of the honey-gland 02mm. long, with 

 some 23 large lenticles (from spiracle to spiracle), and several grand, 

 clubbed, or rather balloon, hairs, almost spherical, and beautifully 

 spiculated ; the flange-hairs possess one very large one, as no segment 

 in front does. The 8th abdominal segment has two very long dorsal 

 hairs (i ?), one 025mm., its fellow 0'18mm., abbreviated, but specially 

 swollen apically in compensation ; there are also, above the spiracles, 

 two lenticles, and five or six balloon hairs ; the presence of the fan- 

 organ is distinct, but its structure is not determined. The 9th and 

 10th abdominal segments have many hairs ; these have, amongst 

 them, a considerable number, of shorter, sharp, apparently hardly- 

 spiculated, hairs ; the hair-bases have striations on their lower halves, 

 but these hardly rise above the surface, and are mere indications of 

 stellate structure. There is no anal plate. The prolegs have one long, 

 and two (or sometimes three) short hooks to each pad ; sometimes two 



