342 STEPHEN G. EICH 



dorsal view of the rectum of Tramea and the \'entral view for 

 Pantala. The large last branch, just cephalad to the postdorsal 

 trachea, is a feature here carried far beyond its extent in the 

 other members of the famil}^ 



Tramea Carolina (figs. 36 and 37) has its gills evenly graded 

 in size, those at the caudal end of the rectum being two and 

 one-half times the size of those at the cephalic end in every 

 dimension. The gill bases show this markedly on the outside 

 of the rectum. There are thirty gills in each single row. Each 

 gill is emarginate along the caudal edge and slightly so on the 

 cephalodistal margin. The epithelial cuvshion is unusually far 

 from the caudal edge, and is rather quadrangular as well as 

 somewhat oblique in position. Figures 36 and 37 show the 

 features of these gills. In all other respects this rectum agrees 

 with that of Plathemis. 



In Pantala flavescens (figs. 31 and 38 to 41) the gills are 

 specialized in a different manner. Of the thirty gills in each 

 row, the last six are twice as high and wide as any of the others. 

 The gill bases change suddenly in size at the same point (fig. 

 31). The twenty-four cephalic gills are all of the same size, 

 but those at the cephalic end are of the same shape as the 

 cephalic gills of Dorocordulia, while the middle fifteen have 

 blunt tops and are much like the gills of Plathemis. Figure 41 

 shows in details a feature found in this genus only: a bunch of 

 five to seven setules near the distal end of the caudal edge. 

 Other features of this rectum are as in Plathemis. 



THE ANAL VALVE 



The perfected respiratory organ of the anisopteran nymph 

 has its means of excluding both harmful liquids and solid par- 

 ticles which might cause injury. To Scott ('05) belongs the 

 credit of first describing this remarkable anal valve; Sadones 

 ('95) seems to have noticed its parts, but not their mutual 

 relations or their function. 



The anal valve of Plathemis lydia was described bj^ Scott 

 as consisting of three meniscus-shaped chitinous lobes projecting 

 into the lumen of the^ rectum at its extreme caudal end, just 



