(Vol. II., p. 31.) Both scales are 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 ob- 

 servers; and, if necessary, I could confirm the fact. In the latitude 

 of Eock 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 Transactions of the Illinois State 

 Agricultural Society (I. pp. 514 — 7) — found them to hatch out about 

 May 23d; at Batavia, Kane coimty, 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 remaining 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 larva 

 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 If times as long as wide; but they were considerably larger 

 than the eggs, of a yellowish color, with distinct beak and antennaa, 

 and ivith 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 ac- 

 quainted, and, as we shall see afterwards, it is an important one both 

 theoretically and practically. At this date the young larvae w^-e 

 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 



