THE GILL-CHAMBER OF DRAGONFLY NYMPHS 331 



Roster ('85) shows an Italian form of Anax that has twenty-two 

 gills to a row and on each gill eighteen villi constricted at the 

 base and bearing a crown of setules at the tip; the other forms 

 have villi more hke A. Junius. Ris ('13) finds in Anax impera- 

 tor gills and viUi identical, so far as his description goes, with 

 those of A. Junius. 



There are certain forms mentioned in the literature of the 

 subject, and labeled 'Aeschna,' which deserve some comment. 

 Dufour ('52) shows a form with semicircular or reniform gills, 

 but lacking villi. I am inclined to think that this is some 

 species of Aeschna, sensu moderno, or a closely allied genus, in 

 which the longitudinal folds were missed; this overlooking of 

 one or another of the sets of folds has been common. Miss 

 Poletajev ('80) , working on a Russian 'Aeschna grandis,' found 

 gills substantially the same as I figure for buttress folds in 

 Basiaeschna, but without any longitudinal fold. Here again I 

 feel sure that something has been overlooked, but I do not know 

 in what genus to place the form described. Ris ('13) assigns 

 gills of this sort to Brachytron hafniense. Sadones ('95), work- 

 ing histologically, reports for an unknown species of Aeschna 

 simple gills with two cushions; this is also an obvious case of 

 omission to see some feature, and the form may be any Aeschnine. 

 • 



D. Subfamily Gomphinae 



In this subfamily I discuss first the rectum of the small nymph 

 of Lanthus, and then four of the typical large burrowers. These 

 latter show great similarity to each other, and connect with the 

 Aeschnine series ending in Anax Junius, but Lanthus stands 

 alone in having what is in many ways the most remarkable rec- 

 tum of any anisopteran form I have studied. 



The rectum of the njonph of Lanthus parvulus (figs. 46 to 48) 

 is smaller than any other rectum in the suborder, and is not 

 over half as long and half as wide as the average. It is perfectly 

 cylindrical, rounded at the anterior end, and tapering suddenly 

 to the long anal canal. The distribution of tracheae to the dor- 

 sal side of the rectum is very much as in Cordulegaster, but the 

 branches orginate as three large branches only, cephalad of the 



