82 FIFTH ANNUAL REPORT 



presently to be treated of, as Dr. LeBaron has already recorded, (Ills. 

 Rep. 1, p. 30), and as I have myself observed. 



We shall also notice that the abdominal joints are each furnished 

 at the sides with two or three spines or stiff hairs, and, upon still more 

 careful examination, we shall find the principal pores through which 

 the substance of the scale is secreted. These have very naturally been 

 overlooked, in the past, by myself and other authors, for they are only 

 visible with great care in the preparation of the specimen, and under 

 the highest microscopic power. I feel quite convinced, from my 

 studies of this and allied species, that a secretion, so subtle and atten- 

 uated as to be invisible, emanates from the general surface; but as is 

 the case so generally with the insects of this and allied families, the 

 bulk of the matter which forms the scale, and particularly the anal 

 portion or shield, is secreted by visible pores upon the posterior por- 

 tion of the body, and which may be noticed at the intersections of 

 the abdominal joints, but more conspicuously in sets just under and 

 around the anus. These anal sets of pores, or secretors as they may 

 be called, are found to vary in position and number according to the 

 species, and have been made use of by Targioni and Signoretto sepa- 

 rate supposed species which are otherwise not easily distinguishable. 

 The number of pores in the different sets is not, however, constant, as 

 will be seen from the description at the close; and should not, there- 

 fore, be too much relied on when unaccompanied by other differ- 

 ences. After careful examination of several specimens of our apple- 

 tree species, I find the median set to consist most commonly of 10, 

 the upper laterals of 20 each, and the lower laterals of 14 each (Fig. 

 32, a). 



We thus see that the larval and medial scales difler materially 

 from the anal shield, in that the two former are composed in part of 

 the shed skins, while the latter is a pure secretion. From the extreme 

 fineness of the threads from which it is formed, they are invisible to 

 the naked eye, and so easily ruptured that the louse always appears 

 separate from its shield when the latter is lifted. Yet, with a good 

 lens, the anal threads may sometimes be seen, especially in the pine- 

 leaf scale to be treated of ; and, strictly speaking, the louse is truly 

 separated from its shell only when the latter is completed and ovipo- 

 sition begins. 



We will now trace the growth of the male scale. Up to the for- 

 mation of the larval scale, there is no perceptible difference between 

 the sexes, but henceforth they are readily distinguished. In the male 

 there is but one other scale formed, and this corresponds not to the 

 second scale of the female, but to the anal shield. It is about twice 

 the length of the larval scale, and though there is a distinct conch- 

 oidal fracture toward the end, which would indicate a short period of 

 rest during its formation, no insections or traces of shed skin can be 

 found. Under this shield the louse gradually becomes a pupa, the 



