TRIFIDM. 227 



hairs ; it has distinct chocolate bands down the back and side, 

 indistinct as to outline, but pronounced as to tint ; it is also 

 olive-brown beneath ; the head has much black ; and on the 

 back, especially on segments five, seven, eight, nine, and 

 twelve, are black tufts rising above the level of the yellow 

 hairs. The long hairs after being bent down parallel to the 

 larval surface are arranged exactly as if they had been 

 brushed smoothly, but they are always brushed forward 

 on the right side, backward on the left — an instance 

 of bilateral asymmetry which *is extremely rare among 

 insects. 



The infant larva is white and brown alternately, segments 

 four and five, seven, eight, nine, and the two last being dark, 

 head black ; second segment with a distinct black plate ; the 

 raised spots, which are conspicuous and mostly black or 

 blackish, have each but one or two hairs ; these are long, black, 

 and longest on the front segments. When half grown the 

 alternation of pale and dark colouring has disappeared, the 

 back of most of the segments has become very dark, almost 

 black, and there are broad purplish and yellow stripes down 

 the sides, but these colours are much hidden by the hairs, 

 which are longer, far more abundant, and of a yellow colour ; 

 head still black, under-surface fuscous. It is not until the 

 fourth moult that the adult colouring is assumed. (Con- 

 densed from the elaborate memoir of Dr. Chapman), 



The southern form of the larva — green with white hairs — 

 is found very frequently upon alder, but most certainly also 

 upon birch ; the yellow and more northern form appears to be 

 more attached to birch; but this may arise from the far greater 

 abundance and wider distribution of birch than of alder. Dr. 

 Freer finds both forms on birch at Cannock Chase, the yellow 

 usually the later in the year — that is in the more slow- 

 feeding larvse probably. Other observers have supposed the 

 yellowness to be a change occurring before the larva spins up, 

 but probably without sufficient reason — the change at this 

 season being to a dirty greenish, with the hairs smoky black. 



