40 
FIRST ANNUAL REPORT OF THE 
very distinct from each other and from the “ anal sack,” and are both of them of a 
yellowish-brown color. In an undescribed species, which maybe called the “Black- 
willow Bark-louse” ( Aspidiotus salicis-nigrce , new species,) and which I find on the bark 
of the Black willow ( Salix nigra,) the perfected scale-insect is of exactly the same size 
and shape as the perfected Oyster-shell Bark-louse ; but, instead of being of the same 
color as the bark, it is milk-white, with the “ larval and medial scales ” pale yellowish- 
brown, precisely as in the Pine-leaf species, and in Harris’s Bark-louse; and moreover 
the eggs under the scale, instead of being milk-white, are blood-red, as in the above- 
named two species. I incline to believe that, throughout this genus, what I have called 
the “ medial scale ” and the “ anal sack ” is formed by the anal surface of the orig¬ 
inal young larva being at two successive periods abnormally dilated and extended 
backwards, in the form of a sack closed at tip ; and that, after this process is accom¬ 
plished, the insect always moults or sloughs off the whole of the external scale, includ¬ 
ing both “larval scale,” “medial scale” and “anal sack,” which has been formed in 
the manner detailed above; and the eggs are then developed inside the scale and at the 
tail end of the moulted insect, and afterwards laid in the ordinary manner under the pro¬ 
tecting scale. In confirmation of this theory, it may be observed here that on August 
15th, I found, under numerous scales of the Ovster-shell Bark-louse that I then lifted, a 
white fleshy, juicy mass still enveloping some of the eggs, and that, under many others 
that I dissected in the autumn, I found towards the small or head end of the scale a 
dried-up mass, (which was apparently the legless body of the mother Bark-louse,) per¬ 
fectly separated from the enclosing scale. In the case of Harris’s Bark-louse, as will be 
shown hereafter, I found under the scale in the autumn, before any of the eggs were 
developed, the living and moving body of the mother Bark-louse, perfectly separated from 
the scale. And in a closely allied species found in Sweden, the description of which is 
quoted from Dalman by Harris, the very same thing is stated to occur. (Injurious 
Insects , p. 255.) So that, in these two cases at all events, it is impossible to believe, as 
most authors have hitherto done, that, at the time when the eggs are developed, the 
outer scale is part and parcel of the living Bark-louse. Neither is it reasonable or con¬ 
sistent to hold with Dr. Harris that, in the case of the Oyster-shell Bark-louse, the scale 
is composed of the dried-up body of the insect, while in the case of Harris’s Bark-louse 
it is a mere cocoon. For in both these two cases the scale consists of precisely the same 
three parts, arranged in precisely the same manner, namely the “larval scale,” the 
“medial scale,” and the “anal sack :” and if it is a cocoon in one case, it must be a 
cocoon in both. But, after all, these matters, though of the highest scientific interest, 
are of no manner of practical importance. 
Hitherto we have spoken only of the mother Bark-louse. I have not actually bred 
the males of the Oyster-shell species ; but there is good reason to believe that a 
small per centage of the larvae — considerably less than five per cent., on a rough 
estimate — which never, like the egg-bearing females, have any long “ anal sack” grow 
out of their tails, subsequently develop into males, and again acquire the power of 
locomotion. Even in the winter time, the empty shells of these individuals may be 
seen still adhering to the bark. Throughout the Bark-louse Family, it is the males 
only that ever acquire any wings, or even any rudiments of wings; and in compari¬ 
son with the females of this species, the males, judging from the minute size of the 
scales out of which they, in all probability, come, must be very small and insignificant 
fellows indeed. The same law obtains throughout the whole Family. 
It is a curious question how a species of insect, which, like the female of this Oyster- 
