TRACHEA IN THE NYMPH OF PLATHEMIS LYDIA. 345 



tion the tracheae appeared as silvery white tubes. Some of the 

 more minute points were worked out teasing with needles under 

 the lower powers of the compound microscope. Glycerine 

 mounts were easily made and studied. 



Tracheal Distribution. 



According to Packard '98 the tracheal system of Plathemis 

 lydia belongs to the peripneustic type in which the prothoracic 

 and abdominal stigmata are present though not functional during 

 the greater part of the larval life. This type is intermediate be- 

 tween the holopneustic or open type and the apneustic or closed 

 type. 



TTti? Dorsals. The tracheal system is most conveniently under- 

 stood by considering first those that lie dorsally, then those that 

 are ventral and those that run laterally. In connection with each 

 of these three systems there will be given an account of their 

 principal branches. The connections of each of the others will 

 be described. The stigmata found dorsally between the pro- 

 and mesothorax will serve as a convenient starting point. From 

 each of the stigmata (Fig. i, STIG] the two largest tracheal 

 tubes, the dorsal tracheae (Fig. I, DORS] extend posteriorly, 

 diverging slightly to the sides of the rectum. There is a small 

 crescent-shaped trachea (Fig. i, CR) arising from the inner face 

 of the dorsals at the stigmata and joining the dorsals again a 

 short distance behind. 



About one fifth of their distance back of the stigmata the dor- 

 sals are connected by a trachea of about one half their own di- 

 ameter (Fig. i, D C). The trachea to the mesothoracic leg 

 (Fig. i, MS 777) arises from the dorsal just back of the above 

 mentioned connective. It receives a branch (Fig. i, MS B) 

 from the dorsal at the stigmata. The tracheae to the meta- 

 thoracic leg (Fig. i, MT 777) arises from the dorsal trachea 

 posterior to the origin of the mesothoracic. The metathoracic 

 also receives a branch (Fig. i, M T 7>) from the mesothoracic 

 trachea. The function of these short branches is not clear. 

 They may serve as stays to hold the meso- and metathoracic 

 tracheae in place. Small tubes pass from the thoracics to the 

 vertical wing muscles. 



