The Apple Mussel Scale. 
169 
numerous slight elevations upon the surface of the bark, each one 
seldom straight, but usually somewhat curved upon itself, either 
to right or to left, sufficiently suggestive of the shape of the 
mussel shell. Its colour scarcely differs from that of the bark to 
which it is attached, though it is a trifle paler. Its length is 
usually between inch and T( %- inch, and its breadth from 
inch to -j-jyjj- inch. Its anterior extremity becomes almost pointed ; 
its posterior extremity is more rounded, is less adherent, and is 
easily raised. The scale 
always presents transverse 
curved lines, concentric 
with the pointed end : these 
denote the successive zones 
of growth. 
The fact that the scales 
are rather more adherent 
at the anterior extremity 
is due to the circumstance 
that the insect here thrusts 
its proboscis, or sucker, 
into the bark for the pur- 
pose of extracting nourish- 
ment. In the early months 
of the year a brownish 
body may be found at the 
anterior end of the space 
beneath the scale. This body, extracted with a needle, is seen to 
be very flattened, and is about T inch long ; it becomes narrowed 
in front, is plainly segmented transversely, and is destitute of 
limbs. This is the body of a female Mytilaspis, dead and dry. 
Behind it there is seen to be a heap of twenty or thirty whitish 
elliptical structures about jJ rxr inch long : these are eggs, and 
between them delicate filaments may be seen to pass. 
This, then, is the state of the Mytilaspis before the larvae are 
hatched out. If, at the beginning of May, the eggs are examined 
under a sufficient magnifying power, the shells are thin enough to 
permit the development of the embryo to be observed. The exact 
date of hatching is determined, of course, by the temperature of the 
surrounding air, and by the total amount of heat the egg has 
received. After the rigorous winter of 1891 in Normandy hatching 
was effected as late as June 6, whilst in 1892 it took place on 
May 20. M. Noel regards the middle of May, however, as the 
mean period of hatching. But, whatever may be the date, the 
larvae never all emerge simultaneously, for the process of hatching 
extends over some days. It is accompanied by the crawling out, 
from beneath the broad end of each scale, of twenty or thirty pale 
whitish larvae, which leave under the scale the crumpled shells of 
the minute eggs from which they have escaped. 
The young creatures are seen to be transversely segmented ; they 
are furnished with a pair of antennae or horns, two reddish eyes, 
Altle Mussel Scale, Mytilaspis pomorum , Douche ; 
A spiel lotus conchiformis , Curtis. 
A, magnified scale, under side, showing female and 
eggs ; B, ditto, showing female shrivelled within 
the scale ; C, apple branch infested with scales— 
natural size. 
