208 The Philippine Journal of Science isis 



molting before the tenth day. The second molt usually occurs 

 after an interval of at least four days, and in some larvae as 

 late as eight days, that is, when 15 to 18 days old. The time 

 of the third molt precedes immediately the appearance of the 

 puparium. This period, as has been noted, shows the greatest 

 diversity among individuals of the brood. The third molt in 

 12 instances was shed between the ninth and twelfth days of life. 

 In other individuals the process was not completed within three 

 months, yet the adult fly was an apparently healthy insect. 



Certain unimportant changes in morphology, dependent on 

 the molting process, are noticeable. The loss in size due to con- 

 traction of the cuticle preparatory to ecdysis is usually compen- 

 sated by a substantial extension immediately following the 

 process. The extent of shriveling of the cuticle is represented 

 by 1 millimeter in the first molting, 1.5 to 2 millimeters in the 

 second stage, and 2 to 3 millimeters preparatory to the third 

 stage. There is a notable increase in length resulting from the 

 second ecdysis. A larva, measuring 22 millimeters on the day 

 previous to the shedding of the skin, measured fully 25 milli- 

 meters the following day. In measurements of this sort one 

 must make allowance for the extraordinary amount of telescop- 

 ing of segments. As much as 5 millimeters may be involved 

 in this process. 



The structures mainly involved in the ecdysis are the tracheal 

 system and the appendages of the head. The anal wing of the 

 trachea constituting the siphon is drawn off in each molt in a 

 perfectly cylindrical form. The body trachea is torn from its 

 connections in irregular strands. The entire head capsule, in- 

 cluding the chitinous pharyngeal framework, the great hook, 

 and other mouth structures, are found in perfect form in the 

 various exuvise. These parts upon renewal in the larva become 

 more heavily reinforced. The exuvia is usually in a good state 

 of preservation; crumpled to be sure, but it can be extended in 

 alcohol to three-fourths the length of the larva. Following 

 each ecdysis, the larva is invariably leaden gray with tracheal 

 strands of waxy white. Three anal segments including the 

 siphon become lead colored and stiffened in structure. They are 

 at this stage more truncated, with an anal band of cuticle 1 milli- 

 meter in depth, making the siphon appear somewhat atrophied. 

 This is no doubt consistent with its restricted function. The 

 color of the viscera has changed from the brilliant red and 

 yellow to an indeterminate white, and the lilac tint of the Mal- 

 pighian tubules has changed to a salmon color. These latter 



