28 



view (Plate V, Fig. 28) shows that it is about as long as the 

 claspers. 



Tracheal System of the Immature Insect. 



The diagram on Plate VI (Fig. 32) illustrates the main branches 

 of the tracheal system of larval and pupal Aleyrodes, based on a 

 study of the two species, vaporariorum and packardi. Prof. C. W. 

 Woodworth has worked out more in detail the tracheal system of A 

 citri.* It will be seen that the diagram here given differs from his des- 

 cription only in a few minor details. What he has called " dorsal gir- 

 dles " I find to be ventral, and his " ventral trunks " I find to be 

 dorsal in the species examined. I have not found the branches 

 which he describes as arising from the transverse connections be- 

 tween the longitudinal trunks and the third pair of spiracles. The 

 following is the explanation of the letters used in the diagram : 



NOTES ON LIFE HISTORY AND HABITS. 



Egg. The mechanical condition of the leaf seems to have some 

 influence on the vitality of the eggs, for if a leaf upon which the 

 eggs have been deposited within five or six days is allowed to wither 

 and become dry, the eggs will not hatch. Those eggs which are 

 nearly mature are not so affected. As a rule, the eggs hatch in from 

 ten to twelve days, though this period may be prolonged by low 

 temperature. On hatching, the egg splits longitudinally from apex 

 to base and the larva slowly frees itself. The egg shell collapses at 

 the same time that the larva escapes, the free edges of the shell 

 curving inward. 



Larva. The newly hatched larva is quite active and may 



* Can. Ent., vol. xxxiii, p. 173. 



