LIFE-HISTORY OF THE ARMORED SCALES. 17 



males agaiu cast their skins ; but their form at this time remains un- 

 changed. The second skin like the first remains in place and forms a 

 part of the scale ; it is, however, less distinctly visible than the first 

 larval skin, being- covered with more or less of the thick excreted ma- 

 terial. 



Soon after the second molt the females are impregnated by the 

 males. From this time until the scales reach their full size their growth 

 is very rapid. In the linear scales (Mytilaspis) the females not only 

 increase in size as their bodies become distended with eggs, but they 

 also shift somewhat their position under the scale, so that finally, at the 

 smaller end, that portion which lies immediately under the molted skins 

 is left vacant. To permit this movement sufficient slack is given the 

 flexible sucking tube between its junction with the body and the point 

 at which it enters the bark. 



The eggs are now laid under the scale, beginning at the outer edge. 

 As they are deposited, the body of the female shrinks, and gradually 

 retreats to its former position, leaving the outer portion of the scale 

 filled with eggs. When all her qggs are laid the depleted female shrivels 

 and dries up, and life in her exhausted body gradually becomes ex- 

 tinct. 



The Males. As crawling larvae, and during the time that their scales 

 are forming, the males are indistinguishable from the females ; but 

 after the first molt differences begin to appear, and the scales of the 

 males become recognizable by their form or color, although the insects 

 themselves are not markedly different until after the second molt. 



Shortly before the second molt of the females the males also cast 

 their skins a second time, and in so doing change to the pupa state. In 

 the pupa, the legs, wings, and other parts of the perfect insect are grad- 

 ually formed under a mask-like skin, in which the new form is obscurely 

 outlined. 



At the second molt the male ejects the skin from its scale, while in 

 the female it remains and forms a part of the scale itself. In the male 

 growth ceases with this molt ; but the scale of the female is at this 

 stage less than half its full size; the male scale is therefore much 

 smaller and thinner than that of the other sex, and the first larva skin, 

 but not the second, forms part of its structure. 



After remaining a week or sometimes less in the pupa state the pupal 

 envelope is rent and torn from its limbs by the perfect insect. This oper- 

 ation takes place under the scale, and the winged fly leaves its shelter 

 only after a rest of several hours, which, indeed, may be prolonged into 

 days if the weather does not happen to be propitious. The exit of the 

 fly is made by pushing up a portion of the outer edge of the scale. In 

 the elongate scales of Mytilaspis, the escape of the male is facilitated 

 by a thin joint in the scale, which permits the broad end to be lifted as 

 a flap. The body of the male terminates in a spine-shaped organ, by 

 (J521 o I -2 



