Imagtnal Rudiments in Thorax 



121 



Until tlie last larval change of skin, wliicli takes place 

 when the larva is of about half its full len2:th, the chief 

 organs already developed which belong to the organization 

 of the future fly are the nervous system and the repro- 

 ductive glands, which grow 

 steadily throughout the larval 

 stage. Soon after the insect 

 enters upon its last larval stage, 

 the rudiments of the head, wings, 



Fig. 90.— Early rudiment of and IcgS of the fly begin to fomi. 

 prothoracic imaginal leg. 



If we take a larva at the be- imagiuai 



n ■ -, . -. . . 1 /-■ rudiments 



ginning or its last stage, 1. e. when it is about half in thorax. 



Fig. 91. — Imaginal rudiments from thorax of larva, more 

 advanced than in lig. 95. The rudiments are enclosed in 

 their capsules (outer walls of invaginations). I, V, I", first, 

 second, and third legs, w, wing, h, haltere. 



an inch long, we shall discover new growths in the 

 thorax, just beneath the skin. An alcohol-preserved 

 larva is best, and we have found it a good plan to 

 divide sach larvae into lateral halves, remove the ali- 

 mentary canal, stain the body-wall with picrocarmine, 



