NORTH AMKRIUAN ODONATA. 201 



The chitinous lining of the rectum of the Anisopterous nymphs 

 is modified so as to present the appearance of six longitudinal bands, 

 rectal tracheal-gilh. Each of these tracheal-gills consists of two rows 

 of thin lamella} in the Libellulidie, of two rows of villous tufts in 

 Aeschna eyanea (Oustalet), or of two rows of lamellse, similar to, but 

 of different shape from those of the Libellulidaj, in Aemlma grandis 

 and juncea (Miss Poletaiew). Into each lamella, or into each papilla 

 of each tuft, run one or more tracheals and split into tracheoles, 

 which run to the apex of the lamella or papilla, recurve and anas- 

 tomose with efferent twigs* The lamellar or papillar tracheals are 

 derived, according to their situation, from a dorsal or a visceral 

 trunk. Each dorsal trunk gives off nine or ten cross-trachete to 

 each of the upper two rectal tracheal-gills of its own side of the 

 body, while the lowermost (ventral) gill is supplied by about eight 

 cross-trachea from the visceral trunk of the same side (Oustalet). 

 The epithelium of the hind-gut of an Aeschna-nymph. has been 

 studied by Faussek (7), who finds it to be of two kinds, sharply dis- 

 tinct from each other: 1, of large cells and nuclei ; 2, of small cells 

 and nuclei. No regularity in their distribution exists ; the smaller 

 cells are found in compact, involved folds, the larger where there 

 are none or only simple, isolated folds. At the extreme hind end 

 of the rectum are six rectal glands, from the simultaneous presence 

 of which, with rectal gills, Faussek concludes with Chun (Abh. 

 Senckb. Natf. Gesell. x, pp. 27-55) in opposition to Gegenbaur, that 

 rectal glands are primitive, rectal gills secondary. The rectal tra- 

 cheal gills are not carried over into the imago (Hagen 27), but as 

 previously mentioned, their vestiges persist. The rectal chamber 

 may serve both for aquatic and for serial respiration, and, by violently 

 ejecting its contained water, for propulsion, and apparently for de- 

 fense (Miss Monks, Am. Nat. xv, p. 141). 



The existence of three rectal-tracheal gills in Caloptenjx, an- 

 nounced by Dufour (Compte Rendu, I'Acad. Sci. T. 29, pp. 764-7, 

 1849), though denied by Miss Poletaiew (29), has been reaffirmed 



« Such is the account given by Oustalet. Macloskie states that the ultimate 

 tracheal ramifications in these lamellae end cpecally, and that the "action of the 

 trachefe is tidal rather than by peripheral capillary circulation" (Psyche iv, pp. 

 Ill, 112, 1883). The results of the writer's examination of the lamellse of a 

 Libellulid nymph and of the caudal tracheal-gills of Lestes agree with tiiose of 

 Oustalet. As, however, the recurrent tracheoles become connected with the 

 twigs from which the efferent tracheoles arise, the peripheral capillary circula- 

 tion, if there be such, must be confined to the loops alone. 



TRANS. AM. ENT. SOC. XX. (26) AUGUST. 1893. 



