• . THE GRAPE PHYLLOXERA IN CALIFOPvNIA. 91 



between the larger female and the smaller male egg, but these inter- 

 mediate eggs are apparently always of the male sex. Thus there is a 

 considerable variation in the dimensions of the male eggs, as, indeed, 

 there is in those of the mature male insects. According to Grassi 

 (11, p. 134—135) eggs producing females vary in length from 0.384 

 to 0.323 mm., and in width from 0.176 to 0.164 mm.; eggs producing 

 males, in length from 0.247 to 0.250 mm., and in width from 0.152 to 

 0.134 mm. He also states that eggs of the intermediate dimensions 

 are fertile and are of the male sex, and that male and female eggs 

 may exceed the limits in one dimension, but never in two. On the 

 average the female eggs were slightly larger than the radicicole eggs 

 and the male eggs slightly smaller, but intermediate eggs had meas- 

 urements identical with those of the radicicoles. 



Measurements of sexual eggs, made in California in 1913, indicated 

 a range in length from 0.450 to 0.257 mm., and in width from 0.171 

 to 0.117 mm. A single female of these hatched (0.357 by 0.171 mm.). 

 In the light of measurements made in 1914 and 1915 it appeared that 

 eggs of the sexes were similar in dimensions to those recorded by 

 Grassi for Italy, except that the range in sizes was somewhat greater. 



The sexual eggs are bright shining yellow. The eggshell is very 

 thin and membranous, quite differently formed from that of the 

 radicicole. The egg hatches after about four or five days' incuba- 

 tion, the process of hatching consisting in the sloughing off of the 

 thin shell, the emerging aphid settling at the place of hatching. 

 The eyes and body segmentation become visible, and the undeveloped 

 appendages are carried under the body. The insect then undergoes 

 four successive molts, and does not move away until it is mature. 

 During the first three instars there appears but little change, except 

 that the body segmentation becomes more distinct. After the third 

 molt the appendages project slightly beyond the sides of the body, 

 but otherwise no visible change occurs. All the molted skins are 

 contained one within another, adhering to the posterior end of the 

 body, and when the last molt has taken place the adult moves away, 

 leaving the " nest " of telescoped skins and eggshell behind. It 

 sometimes happens that the adult is unable to cast off this pad of 

 skins. The mature sexuals are capable of running actively, and, 

 according to European investigations, they may live for some weeks, 

 thereby facilitating a meeting of the sexes. The sexuals take no 

 nourishment. The female is slightly larger and the male slightly 

 smaller than the newly hatched radicicole. 



DESCRIPTION. 



THE SEXUAL FEMALE. 



Orange or orange yellow ; antenna? and legs dusky grayish ; antennae longer 

 than those oj newly hatched radicicole. Body a little longer and wider than 



