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{Aspidwtus salicis-nigrcVj new species,) and which I find on the bark 

 of the Black willow (Salix nigra,) the perfected scale-insect is of ex- 

 actly 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, pre- 

 cisely 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 original young 

 larva being at two successive periods abnormally dilated and ex- 

 tended backwards, in the form of a sack closed at tip ; and that, after 

 this process is accomplished, the insect always moults or sloughs off 

 the whole of the external scale, including 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 protecting scale. In confirmation of this theory, 

 it may be observed here that on August 15th, I found, under numer- 

 ous scales of the Oyster-shell Bark-louse that I then lifted, a white 

 ileshy, juicy mass still enveloping some of the eggs, and that, under 

 man}^ others that I dissected in the autumn, I found towards the 

 small or head end of the scale a dried-up mass, (which was appar- 

 ently the legless body of the mother Bark-louse,) perfectly 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. (Ifijurious 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 consistent 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 of these two cases the scale consists of precisely the same 

 three parts, arranged in precisely the same manner, namely the "lar- 

 val scale," the "medial scale," and the "anal sack;" and if it is a co- 

 coon 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. 



