THE GENUS ACRONYCTA AND ITS ALLIES. 
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double segment are represented by the 7 nentuni 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 Acronyctas 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 
