'29S DAVENPORT ACADEMY OF NATURAL SCIENCES. 



their enemies flaring the previous years. During the years 1873, 1874, and 

 1875 tliey were scarcely noticed at all. In 1876 they again became suflS- 

 ciently abundant to attract general attention, and in 1877 and 1878 they 

 were as plentiful as in 1870 and 1871, only more extensively distributed^ 

 being found as far as twenty blocks from the starting point in 1867. In 

 1879, through tiie increase of their enemies and the depletion of their 

 food trees, they have decreased considerably in numbers and vitality. 

 During the last three years I have given a good deal of attention to this 

 insect, and the rpsults of my studies are given in the following pages. 

 I have also published a brief article in the Davenport Daily Gazette for 

 .June nth, 1877, and another in the Transactions of the Iowa Horticultural 

 Society tor 1877, Vol. 12, pp. 317-324, Des Moines, 1878. Having traced 

 the complete circuit of its life for three generations, I will begin my 

 account with the period at which it first becomes an independent crea- 

 ture. 



THE EGG. 



The Egg, tig. 18, is regular oval in form, nearly elliptical, about 303 p* 

 in lengtii and 180 /Jt in breadth, the greatest breadth being a very little 

 in front of the center. When very higiily magnified it is seen to be cov- 

 ered, more or less closely, with minute circles, tig. 18, a. These last ap- 

 pear to l>e the dust-like, waxy secretions of the ventral abdominal pores, 

 which have become attached to the egg shell ^y means of a viscid sub- 

 stance. po.ssibly secreted by the vaginal glands shown in tig. 47. The 

 eggs found in the ovaries are without this ornamentation. 



When first laid, the egg is of a pale yellowish white color, but becomes 

 very much darker, as the embryo becomes fully developed. This color 

 comes mainly from the embryo showing through, as the egg-shell is nearly 

 colorless and transparent. In this locality the first eggs are laid during 

 the last part of May. varying from the 18th to the 25th, according to the 

 weather, and the egg-laying continues from five to seven weeks accord- 

 ing to the health of the mother. 



THE EMBRYO. 



At the earliest stage noticed, Fig. 17, the yolk appears to be somewhat 

 contracted, leaving a small, apparently vacant space at each end, and to 

 l>e inclosed by a thin layer of granular substance with a gathering of 

 granules at eacij end. One of these, larger than the other, appears to be 

 at the head end. I failed to observe any nucleus or germinal vesicle 

 at any stage, probably because I did not know how to look for them. 

 It is probable that the gatherings of granules at the two ends may repre- 

 sent the first stages of segmentation. 



The collection of granules at the head end grows most rapidly, extend- 

 ing gradually further and further downwards through the yolk. It has 

 the appearance of being a hollow sack, denser at the sides and in the 



*In this pnper I have talien the 1-1000 of a millimeter, equal to 1-25400 of an inch, 

 indicated by U) as the unit for meaeurement, thus 4 « is a little less thau 1-1000 of an inch. 

 The measurements tj'ven f<houl<l be regarded as approximate rather than absolute, though I 

 believe they will be found correct within the ranj^e of individual vaj-iiitions of the insects 

 themselves- 



