ACTING STATE ENTOMOLOGIST. 37 
from the other ?” The answer is short and simple. The scale of the Oyster-shell Bark- 
louse is the shape of a very elongate pear, considerably hunched, and of the exact color 
of the bark. That of Harris’s Bark-louse is usually the shape of an egg, almost entirely 
flat, and of a pure milk-white color. Lift up the former with the point of a penknife any 
time between the middle of September and the middle of May, and you will see under¬ 
neath it a score or two of very minute milk-white eggs, many of which will often di op 
out and on any dark surface look like so many grains of corn-meal. Lift up the latter 
in the same manner and at the same period, and you will find that the eggs, though of 
the same size and shape as those of the other species, are not milk-white, but blood-ied. 
If these distinctive characters are not sufficient — and they certainly ought to be suffici¬ 
ent in all conscience — the reader can refer, in addition, to the figures of the two kinds 
of scales given in the Practiced Entomologist , (Vol. II. p. 31.) Both scales aie alike in 
being about one-eighth or one-tenth inch long. 
The Oyster-shell Bark-louse is not double-brooded, as Dr. Harris erroneously 
supposed, but single-brooded. That point is now conclusively settled by the unanimous 
testimony of many recent observers; and, if necessary, I could confirm the fact. In 
the latitude of Bock Island, the eggs hatched out about the 4th of June in 1867, the 
spring of that year being unusually backward. In McHenry county in 1854 Dr. E. G. 
Mygatt — who published an admirable Paper on the habits of this insect in the Transac¬ 
tions of the Illinois State Agricultural Society (I. pp. 514 — 7) — found them to hatch out 
about May 23d; at Batavia, Kane county, about May 17th; and at Oswego, Kendall 
county, on May 18th. “ But,” as he adds, “ in no case were they found till after the 
apple-blossoms had fallen, and the young fruit commenced growing —it is vain to look 
for them before.” Of course, the time of hatching will vary somewhat with the season 
and the latitude ; but Dr. Mygatt’s rule will probably be found sufficiently accurate for 
all practical purposes. According to my Journal, my apple-trees were in full blossom 
on the 26th of May in the year 1867 ; so that by June 4th, the date when most of the 
young bark-lice were hatched, the young fruit must have been just about set. I noticed 
that on May 31st, or four days before the general hatch, although not a single egg had 
then hatched, some few of them —perhaps one out of every 40 or 50 —instead of re¬ 
maining milk-white had turned yellow. Changes of this kind are quite usual with 
the eggs of different kinds of Bark-lice shortly before hatching-time ; for I have myself 
observed in the case of several distinct species, that the color of the future laiva often 
shows through the translucent shell of the egg a few days before it hatches out. The 
young larvae on June 4th, when observed under the lens, were nearly of the same oval 
shape as the eggs, that is to say about 1% times as long as wide ; but they were consid¬ 
erably larger than the eggs, of a yellowish color, with distinct beak and antennae, and 
with their three pairs of legs equidistant at their origin from each other. This last character 
I have found to be universal in the larvae of all the numerous kinds of Bark-lice with 
which I am acquainted, and, as we shall see afterwards, it is an important one both 
theoretically and practically. At this date the young larvae were scattered so densely 
over the bark, that it looked as if it had been sprinkled with fine corn-meal; and at a 
casual glance no one would suppose them to be living animals, were it not for the fact 
that many of them might be seen, even with the naked eye, to crawl slowly along, 
having the appearance of little moving pale dots. Seven days subsequently, and proba¬ 
bly sooner, these larvae had all become stationary, and never moved afterwards from the 
point in the bark to which they had attached themselves. At this date, they presented 
under the lens the appearance of conspicuous, flat, white scales, oval and one-tliird 
