ACTING STATE ENTOMOLOGIST. 
39 
assumed its permanent shape ; and what remains now of the original body of the larva 
forms merely a minute, yellowish-brown, oval plate, pressed down obliquely upon the 
forward end of the so-called scale-insect, just as one of these stylish modern trenclier-caps 
is pressed down upon the forehead of a fashionably dressed young lady in the yeai of out 
Lord 1867. Examine the Oyster-shell Bark-louse when you will, from the middle of 
August to the middle of the following May, and you will find it is externally always the 
same. In front there is what is left of the originally perfect, but now degiaded and 
defunctionate larva, being an oval scale, of a somewhat shining yellowish brown coloi, 
and with one longitudinal ridge running from end to end, on each side of which are 
several indistinct transverse grooves, being all that remains to indicate that this was 
once a highly-organized animal, divided by the usual transverse sutures into the normal 
13 segments found in the larva of almost every insect. Behind this yellowish-brown 
cD 
scale —which I shall for convenience’ sake call “ the larval scale”—may be seen a 
rather longer and wider one — which I shall call “the medial scale” without an\ 
ridges or grooves and of the same opaque greenish-brown color as the bai k, but often, 
especially at its hind end, tinged more or less with yellowish; and behind this again, 
and closely connected with it, the rest of the enormous elongated sack protiuded in the 
space of about two months from the tail end of the larva, which is always of the same 
greenish-brown color as the bark. This posterior sack, which I shall call the “anal 
sack”, is in its widest part about twice as broad as the “larval scale” is long, and, 
together with the “ medial scale,” is from 4 to 10 times as long as the “ larval scale, 
but most commonly about 8 or 10 times as long. If the whole scale-insect is lifted up 
by the point of a penknife about the middle of August, the white eggs previously 
referred to may be found underneath it, the delicate part of the protruded sack that 
adheres to the bark being usually more or less torn open by the operation; and the 
eggs remain under the scale, without further development, all through the wintei and 
until the middle of the following May. In the course of the winter they doubtless 
freeze and thaw, and thaw and freeze, scores of times; but, as with almost all insects 
when they are hybernating, this produces not the slightest effect upon their vitality. 
Authors, who have never traced a Bark-louse day after day through all these aston¬ 
ishing transformations, have erroneously hinted that the “ larval scale ’ lepiesents the 
head, that the “medial scale ’’represents the thorax, and the large “anal sack 
behind the whole represents the abdomen of a normal insect. (See Fitch, New Yoi Jc 
Reports, I. p. 257.) But no such thing can possibly be ; for there is externally no per¬ 
ceptible change in the “larval scale,” except a verj T slight one in size, from the days 
when the first rudiments of the “ medial scale ” and of the “ anal sack ” are protruded 
from behind it, to the day w'hen both are fully developed. Consequently, as the ‘ lai- 
val scale ” represented originally both head, thorax and abdomen of a normal insect, 
and as it ever afterwards remains unchanged, it cannot afterwards represent the head 
alone of a normal insect. 
What may be the precise nature of this singular “ medial scale ” and “anal sack,” is 
hard to tell with absolute certainty. They are not, however, peculiar to the Oyster- 
shell Bark-louse, but are characteristic of the whole genus ( Aspidiotus ,) to which both 
this species and Harris’s Bark-louse belong. In a very elongated and narrow species of 
the same genus, the Pine-leaf Scale-insect, ( Aspidiotus pinifolice, Fitch,) lound on the 
leaves of the White Pine ( Pinus strobus ) — which, by the way, I have ascertained to con¬ 
tain in November eggs of the same blood-red color, as those of Harris’s Bark-louse the 
“anal sack” is of a pure milk-white color, and the “larval and medial scales” are 
