THE TERRAPIN SCALE. 41 



mination. They finally reach the tips of the twigs, where they locate 

 by preference upon the basal part of the young growth. Many, how- 

 ever, locate upon 1-year-old wood, and a few upon the 2-year-old 

 wood. Other parts of the tree are very seldom infested. The larvse 

 settle by preference upon the underside of horizontal limbs and upon 

 the unshaded side of vertical branches. There is a tendency for 

 them to group themselves in rows upon the illuminated sides of the 

 twigs. The individual scales within these rows are not necessarily 

 in alignment, either with their neighbors or with the axis of the twig. 

 This linear arrangement results solely from their instinctive desire to 

 locate in the area of greatest illumination, which, from the nature of 

 the twigs upon which they locate, is always many times longer than 

 wide. During migration the mortality is very low. 



The females are very flat and have the pale yellow color of the pre- 

 ceding stages. This color appears rather lighter than in the second 

 instar, due, no doubt, to the effect of the nearly transparent dorsal 

 scale. The only colored portions at this time are the brown eye- 

 spots and the chitinized anal plates. 



Specimens measured in 1912 and in 1913 were from 1.23 to 1.57 

 mm. in length and from 0.65 to 1.12 mm. in width, the average 

 height being about 0.1 mm. The average size for both seasons was, 

 length 1.47 -mm., width 0.98 mm. 



The Female Upon the Twig: Development During the First 20 Days. 



After attaching to the twigs the young females begin a period of 

 rapid growth. A small red blotch, which appears over the oral region 

 either during the migration or immediately after it, begins at once to 

 enlarge and to form itself into a narrow band of a reddish-brown color 

 which extends backward along the middorsal line until by the sixth 

 day it reaches the anal plates. (Fig. 15, a.) Meanwhile the dorsum 

 changes from a flat to a mildly arched surface and the larva increases 

 from about 1.54 to 1.65 mm. in length and in width from 1.03 to 1.29 

 mm. When the dorsal band reaches the anal plates it forks. Each 

 fork when developed equals the original band in width and is slightly 

 longer than wide. These forks start about the sixth day and are 

 about one-half completed by the eighth day. From the sixth to the 

 tenth day there is a very decided arching of the dorsum. Growth is 

 greatest just in front of the anal plates, and the elongation of the 

 dorsum at this place first constricts and then breaks the dorsal band, 

 leaving a short piece of it attached to the forked portion that is form- 

 ing about the anal plates. (Fig. 15, b.) Later the anterior piece is 

 displaced forward and shrinks until it becomes inconspicuous just 

 above the oral region. About the eleventh day after migrating, the 

 forks of the dorsal band are completed. This band is a secondary 

 sexual character, which, after copulation, fades and blends with the 



