338 BRITISH BUTTERFLIES. 



icarus l'2mm., coridon l'5mm., argus (aeyon) 1-Omm., and even 

 minimus 0*84mm. Admitting that my measurements may not be 

 accurate, these here given, made in a similar way, are certainly 

 comparable. 



This small size of head implies that the feeding of the larva in this 

 stage is in some unusual manner, and also that that manner, whatever 

 it is, does not require greater power and energy on the part ot the 

 larva, than is usual, but probably much less. It lends, therefore, some 

 support to the idea that throughout this stage the larva is in some 

 way supported by, or at the expense of the ants and not in the 

 ordinary way of eating vegetable tissues. The eating done in this 

 stage in the autumn seems to be negligeable, yet the jaws are of typical 

 form, not modified in a predacious direction, as if it fed on ant larvae, 

 nor on the other hand degenerated as if the larva was actually fed by 

 the ants. It seems to emphasise without in any way clearing up the 

 mystery attending this period of the larval life. 



When hatched the larva is of pale greyish colour, it soon becomes 

 reddish and, except in the matter of size, the following description 

 taken from a second stage larva would apply to each stage: " Short 

 and thick and of nearly uniform size, from end to end 2 , 3mm. long. 

 Flesh colour with darker, almost red markings, head black, prothoracic 

 plate grey and black ; seen laterally, however, there is a regular 

 tapering from third abdominal segment to posterior extremity. The 

 red markings are a broad dorsal band, an upper very fine and a lower 

 broader oblique line, then red above the nearly white lateral flange, below 

 which there is again a darker, followed by a pale band. The full- 

 grown larva (before hibernation) is only 5 or 6mm. long. 



When the larva of avion in its fourth (last) instar disappears for 

 hibernation it is very small, suggesting that it is in the same early 

 instar in which so many other larvae of blues enter into hibernation ; 

 these others have, however, further instars to assume after they come 

 out to feed in the spring. L. avion larvae, when found in the spring 

 as a large fat larva, of larger size than a full-grown larva of icarus or 

 covidon, is nevertheless still in the same instar as it was in on its 

 autumnal disappearance. The proof of this is to bo found in a com- 

 parison of the head, legs, prothoracic plate, and hairs and their bases 

 of the two larvae. The only difference is that the hair bases on the 

 autumnal larvae are most closely packed together, more so than is so 

 usually the case in larvae of blues immediately after a moult. On the 

 spring larva the hair bases are widely apart, the skin between them 

 being well-developed, or extended ; in the autumnal larva there was 

 no skin visible, so closely are the hair bases packed together. 



These facts are demonstrated on pi. xli., figs. 1 and 2, which show 

 the heads of the autumnal and spring larvae at the same magnification, 

 viz., x 50. 1. the autumn larva? ; 2. the full-grown larva (somewhat 

 distorted and damaged). PI. xxxvii., the prothoracic plates : 1. of the 

 autumn, 2. of the full-grown larva x 100. In fig. 1 the hair-bases 

 are so closely packed that the whole prothorax comes into the picture. 

 In fig. 2, the full-grown larva, there are comparatively few hair bases, 

 the greater part of the area being the intermediate skin. I ought to 

 say here, by parenthesis, that the full-grown larva I had was, from the 

 point of view of mounting on a microscopic slide, in a very dirty con- 

 dition, and my efforts to clean it left it a good deal damaged, and still 



