TRACHE.E IN THE NYMPH OF PLATHEMIS LYDIA. 



351 



a millimeter in length. Oustelet, '69, estimates that there are 

 twenty-four thousand respiratory folds in the larva of sEscluia 

 cyanca. These folds are not flat enough to be called gills ; they 

 are more like papillae, but they serve the same function as gills. 

 There are certainly as many in the rectum of Plathemis lydia. 

 By the great number of folds or gills the surface area of the 

 rectal breathing apparatus exposed to the water is increased 

 roughly speaking about eight or ten times. As previously indi- 

 cated the dorsal trachea after many subdivisions divides into two 

 sets of tracheae (Figs. I and 2, R T), a dorsal set and a lateral 

 set (Fig. 4, Z>), supplying the dorsal and lateral rectal gills. 

 The fine subdivisions of the ventrals pass to the ventral rectal 

 gills. The final disposition of the finer tracheoles to the gill 

 itself is shown in Fig. 7. In this figure four gills are shown teased 

 apart. Each tracheole (Fig. 7, G 7") bifurcates just before it 

 reaches the upper edges of two adjacent gills of the same side. 

 One branch (Fig. 7, P] passes to the posterior edge of one of the 

 gills, while the other branch (Fig. 7, A) passes to the anterior 

 edge of the gill behind. Each of these branches sends finer 

 tracheoles into the gill. These divide and fill the gill in its most 

 expanded portion with a network of tracheae. 



Examination under high power shows that the tracheoles 

 (Fig. 8, 7") from the posterior and anterior gill tracheae form 

 loops overlying one another (Fig. 8, AA ). The condition in 



GT 



RG 



FIG. 7. 



FIG. 8. 



Plathemis lydia then confirms the work of Sadones, '95, who 

 found in the Odonata he studied that the gill tracheoles were 

 found in loops and therefore connected. A close examination of 

 his figures, however, shows that he has drawn the tracheae end- 

 ing blindly and not in loops. 



