TRACHE.E IN THE NYMPH OF PLATHEMIS LYDIA. 343 



Odonata. The Libel lulidre are among the most highly organ- 

 ized of the Odonata. As far as the tracheal system is concerned 

 Platlieinis lydia is well classified. The nymph is aquatic, 

 inhabiting the muddy bottoms of quiet pools. It has a swift 

 darting motion when disturbed, caused by expelling water from 

 the rectum. The average length of those studied was 23 mm., 

 the width 7 mm. The head is marked by the large eyes at the 

 upper outer angles ; a single pair of short antennas extend from 

 below and between the eyes. The prominent mask, a modified 

 labium, covers the mouth parts. There are three pairs of legs, 

 all attached to the thorax, which also bears dorsally two pairs 

 of short functionless wings. Anterior to these is a single pair 

 of prothoracic stigmata, functionless also. On the abdominal 

 segments are found seven pairs of functionless stigmata. Inter- 

 nally the alimentary canal extends from mouth to anus and con- 

 sists of esophagus (Fig. I, E), stomach (Fig. I, ST], intestine 

 and rectum (Fig. I, A"). At the junction of the stomach with 

 the intestine are the malpighian tubules. On the dorsal face of 

 the gut over the rectum and stomach is the slightly lobed blood 

 vessel. On either side of this and somewhat posteriorly are the 

 immature reproductive organs. 



Ventral to the gut is the chain of seven abdominal ganglia 

 (Fig. 2) the posterior being the largest. The ganglia are con- 

 nected by nerve cords to each other and by the same method 

 anteriorly with the thoracic ganglia (Fig. 2). There are three of 

 these not fused, the meta- and mesothoracic being nearer together 

 than the meso- and prothoracic. The prothoracic ganglion con- 

 nects by nerve cords with the subesophageal ganglion and this 

 by the esophageal ring with the dorsally lying brain (Fig. I, hi*). 

 On the upper outer sides of the brain are the large optic lobes. 

 It is the tracheal distribution to the foregoing parts that I have 

 worked out and also the connections and interconnections of the 

 tracheae. 



METHODS. 



i 



The nymph was placed in a strong solution of glycerine in a 

 watch glass and the dissections made with small scissors and 

 needles sharpened down to cutting edges. Most of the work 

 was done with a dissecting microscope. In the glycerine solu- 



