THE GENUS ACRONYCTA AND ITS ALLIES. 127 



double segment are represented by the vientum or by the 

 " chin-gland," I do not know. 



The rest of the larva is black, dorsally with a greenish-blue, 

 almost metallic tint, laterally and beneath with a brownish, 

 bronzed tone, it is elaborately wrinkled, the grooves having a 

 bluish bloom. The wrinkling is pronounced about the spiracles 

 and the spiracular tubercles, forming a lateral raised ridge, 

 until the larva is quite full-fed, when this is filled out and 

 tolerably level, and the finer wrinkles only are to be discovered. 

 The spathulate hairs are on either side, two and a short one 

 on 2nd segment, and one each on 5 to 10, 12 and 13. They 

 are spathulate, not clavate, that is, the enlarged end is flattened, 

 the flat sides being dorsal and ventral. The circum-spiracular 

 and marginal tubercles are also present, each with a minute 

 blackish-brown hair. 



All the other British Acnmyctas have normally 5 moults, 

 unless, perchance, strigosa is to be regarded as an exception, 

 alni has only 4. But, whilst several of them, probably all, 

 do upon occasion have only 4 moults, so alni does sometimes 

 have 5 ; and, when it does so, the larva in the extra, penul- 

 timate skin, differs from any of those already described, and 

 shows a transition between the juvenile and adult plumage, 

 showing that formerly the adult plumage was attained by a 

 gradual development, and that the abrupt transition occurs by 

 the suppression of the now lost intermediate stages. One 

 form of extra skin is like the present 4th, with certain adult 

 characters superadded, of this form I have seen a good many. 

 Another form has only been observed in one specimen, and is 

 more like the adult than the juvenile form, but with some 

 juvenile characteristics. 



Of the former of these two forms, I have noted that out of 

 about 250 larvae, half had spun up and only some 15 were not 

 in last skin ; of these 15, 4 were extra moulters, and of the 

 remaining ii, three were certainly not extra moulters, and 

 several were likely to die of atrophy, how many of the others 

 became extra moulters I have not recorded. It would thus 

 appear, and I have observed a similar circumstance in other 

 species, that a larva, belated by want of food or other circum- 

 stances, may die of atrophy, or may display extra vigour, have 

 an extra moult, and finally be a larger specimen than if the 

 usual normal course had been pursued. 



Roughly, the larva in extra 5th skin resembles that in 4th 

 skin, but is larger, and differs in colouring. It has a dark 



