2 9 



crawl some distance before settling down, or may remain quite near 

 its place of birth. Its rate of locomotion on a leaf is between one 

 and two millimeters per minute, equivalent to about one-half an inch 

 in ten minutes. The larvae rarely crawl in a straight line, however, as 

 they double on their own tracks and change direction at every little ob- 

 struction such as a hair or a particle of dirt on a leaf, so that it is a 

 rare accident if one finally reaches a distance of one-half inch before 

 settling down, where it remains until it reaches the adult condition. 

 Everything considered, there seems to be little chance of an Aley- 

 rodes in this instar getting from plant to another, or even to another 

 leaf, unless the leaves are in actaal contact. The young larva usu- 

 ally settles down within twenty-four hours and gradually loses the 

 use of its legs. 



The duration of the first instar is from five to seven days, of the 

 second and third instars from four to six clays each, and of the fourth 

 or pupal instar from thirteen to sixteen days. At moulting, in the 

 first three instars, the skin splits apparently around the anterior 

 margin of the body, and is then gradually moved back, aided by up 

 and down movements of the abdomen, and usually drops off entirely 

 unless entangled by the hairs of the leaf. Moulting appears to be 

 a slow process, from two or three hours to a whole day being re- 

 quired before the change is entirely completed. As each portion of 

 the body becomes freed from the skin it spreads out over the surface 

 of the leaf and immediately assumes the form and horizontal dimen- 

 sions which continue throughout the instar. 



If the ventral surface of a freshly moulted insect of the second, 

 third or pupal instars be examined, it will show a large fleshy pro- 

 jection arising on each side between the bases of the first and second 

 legs. These structures are concave at the tip, and are probably ad- 

 hesive in function, serving to keep the insect attached to the leaf 

 during the process of ecdysis, as they disappear soon after. A 

 specimen in the second instar, placed on its back on a glass slide, 

 was observed to withdraw these almost completely within five min- 

 utes. 



Changes in position of the Aleyrodes in the second, third and 

 pupal instars are very slight, if any, and these occur only at the time 

 of moulting, or immediately afterward. In one instance, one of 

 these insects in the third instar was observed to move in the course 



