THE GILL-CHAMBER OF DRAGONFLY NYMPHS 319 



Cuvier (1799) was the first to investigate the structure of the 

 gill-chamber. In an 'Aeshna' (which probably was Anax im- 

 perator), he found twelve rows of gills bearing villi in the much 

 enlarged rectum and observed fine tracheal branches in the 

 villi. 



Haussmann (1803), Sprengel (1815), Marcel de Sorres (1818), 

 and Meckel ('29) add nothing but curious errors. Suckow ('28) 

 describes with more accuracy than any one preceding him the 

 rectum of another species of Anax. 



The more adequate study of the anisopteran rectum begins 

 with the work of Leon Dufour ('49, '52). In the first paper 

 Dufour claims that the zygopteran nymphs also have rectal gills, 

 but later admits that there are such only in Calopteryx. He 

 treats in detail two aeschnine species and one libellulid. Hagen 

 ('52), summarizing the work up to that date, corrects the crude 

 taxonomy of Dufour, for whom, as for most of his precursors, 

 every big aeschnine nymph seems to have been ^4eschna grandis.' 



The work of Oustalet ('69) set a new standard of precision 

 in observation. He described with care the distribution of 

 tracheae from the main trunks to the rectum and figures this 

 well. In Anax and Libellula he adds a number of details of gill 

 structure, being the first to describe the loops of tracheoles in 

 the gills. He notes also the existence of a distinct anal canal in 

 the Aeschninae only. 



Since the work of Oustalet, some nineteen papers have been 

 written on this subject. The most important are those of Chun 

 (!77), in which epithelial cushions are first noted; Poletjev ('80) 

 described several new forms of gills; Sadones ('95) gives a fine 

 histological study of the whole alimentary tract of Libellula 

 depressa. Scott ('05) described the tracheation of the nymph 

 of Plathemis lydia; Ris ('13) described gill forms of ten genera 

 and some features of their rectal anatomy, but without figures; 

 and Oguma ('13) described the disappearance of the gills during 

 metamorphosis. 



Specimens of the following genera have been examined by the 

 workers above quoted: Onychogomphus, Gomphus, Aeschna 

 (S. lat), Brachytron, Anax, Cordulegaster, Epitheca, Cordulia, 

 Sympetrum, Libellula, Plathemis. 



