80 



With such a correlation of the sexes, in freedom, by far not all the 

 females can become fertilized (although one male usually fertilizes two 

 females), and consequently the greater part of them lay their eggs non- 

 fertilized. 



Nature having provided the blood louse with a powerful means of 

 preservation of its species, namely, with parthenogenetic multiplica- 

 tion, left the sexual mode of multiplication, as it were, in reserve only 

 (as auxiliary), not having perfected it to the necessary degree. 



Thus, although the winged blood lice are capable of flying over to 

 uninfested trees, the sexual females produced by them, owing to a lack 

 of males and the difficulty of finding the females by the latter, lay, in 

 the majority of cases, unfertilized eggs. 



The males and females of the blood louse, as is well known, have no 

 proboscis and digestive organs and do not take food during the whole 

 of their life, which lasts, according to my observations, fifteen to 

 eighteen days. In the course of that time the sexual individuals grow, 

 moult several times, and are in constant motion. 



The adult female is of a convex, ovate form, yellow red in color, with 

 dark eyes. The antenna? are rather short, five-jointed; the first two 

 joints are the shortest ones; the following three are longer and nearly 

 equal to one another; the last joint is somewhat pointed. The adult 

 female is twice as large as the male; she is 1.1 mm. long, 0.5 mm. wide. 



The male is better shaped and quicker in the movements than the 

 female; five-jointed antenna?, about half as long as the body; the third 

 and fifth joints are of about the same size; the fifth one has a hollow 

 and is pointed. The color of the body is olive yellow. On the last seg- 

 ment of the abdomen there are two pointed sexual stripes. The length 

 of the adult male is 0.5 to 0.7 mm., the width, 0.2 mm. Both sexes are 

 covered with a slender white down. 



About twelve days after birth the females become slow in their move- 

 ments. When not at freedom (as in experiments), they gather at the 

 lower surface of the leaves and into depressions of the latter. Through 

 the integument of the adult female begins to shine through a large, 

 long, oval egg, constantly increasing and filling the whole cavity of the 

 female. 



About this time the mobile males hunt up the females for pairing; 

 the male gets upon the back of the female, and in this position the in- 

 sects remain more than an hour. One male fertilizes two, but some- 

 times more females. Two days after the pairing the female lays its only 

 egg, performing this act slowly during fifteen or more minutes, owing 

 to the enormous size of the egg as compared with the insect itself. The 

 laying of the egg appears as the last act in the life of the sexual female, 

 from which there remains almost nothing more than the shriveled skin, 

 of an olive yellow color, which continues to move for some time. 



The egg of the blood louse recalls to one that of the phylloxera. It 

 is oblong, cylindrical, rounded at the ends; freshly laid it is smooth, 



