TRACHE.E IN THE NYMPH OF PLATHEMIS LYDIA. 347 



I, />) pass forward into the brain, indicating that a considerable 

 amount of oxygen is used in the metabolism of this organ. At 

 the place where the loop joins the cephalic tube two branches 

 arise together one the optic (Fig. I, 0) passing out to the optic 

 lobes (Fig. i, L] and the eyes. The other to the trophic (Fig. 

 I, T) passes down underneath the optic lobes and on out to 

 the head parts. 



Posterior Dorsals. The dorsals give rise to branches supply- 

 ing the alimentary tract the blood vessel and reproductive 

 organs and other adjacent tissues. 



Posteriorly the dorsals become much smaller in size, this 

 being due to the fact that each gives off many smaller tracheae 

 to the dorsal and lateral surfaces of the rectum (Fig. i, RT\ 

 Most of these after much subdivision into fine tracheoles pass 

 through the wall of the rectum to the rectal gills. One of the 

 larger branches of the dorsal continues back as the post-dorsal 

 (Fig. I, P -D), then passes down over the side of the rectum join- 

 ing the post-ventral (Fig. I, P V], which curves forward and 

 inward on the ventral surface of the rectum connecting with the 

 main ventral tracheal tubes (Fig. 2, VENT}. At the place 

 where the post-dorsal meets the post-ventral the former contin- 

 ues posteriorly up over the dorsal surface of the rectum (Fig. 

 i, PC). 



TJie Ventrals. Arising from the post-ventral the ventral 

 tracheae (Fig. 2, VENT) pass forward on the ventral surface of 

 the rectum toward the mid line and diverge as they continue on 

 the under surface of the stomach. At the anterior end of the 

 stomach each ventral curves up and around crossing over the 

 upper surface of the stomach. The right ventral finally joins the 

 left mesothoracic trachea just beyond the latter' s origin from the 

 dorsal. Also the left ventral joins the right mesothoracic in a 

 similar manner (Fig. CR V). Fig. 2 is drawn with the an- 

 terior part of the stomach removed to show the union of the ven- 

 tral with the mesothoracics. It will be noted that the ventrals 

 arising from the dorsals posteriorly join them again anteriorly. 

 From the posterior ends of the ventrals tracheae run to the ven- 

 tral surface of the rectum and through to the rectal gills. In 

 front where the ventrals are near together they send branches to 



