IN THE LARV^ OF ANISOPTERID DRAGONFLIES. 129 



Ratzebnro- (21). But it was Dufonr (5) who made the first real advance in 

 the knowledge of the true nature o£ these organs. He showed that trachese 

 penetrated into the projecting folds of the rectum, which thus are actually 

 of the nature o£ tracheal gills. To Dufour also we owe the first definite 

 assertion that the complicated rectal breathing-apparatus studied by bim in 

 the larvse of Lihcllula and ^sclina did not occur in the Zygoptera. His 

 discovery of three longitudinal folds in the rectum of Calopteryx, which he 

 considered to be poorly developed breathing-organs, does not concern us 

 directly here. But, as this function has been denied to them by recent 

 authors, we may well point out that this aspect of the problem needs fuller 

 investigation. 



After Dufour, the subject was briefly touched upon by Milne-Edwards (17) 

 and Leydig (12). The latter author was the first to discover the important 

 fact that the finest tracheal capillaries ramifying in the gills do not end 

 blindly in them, but form complete loops. Leydig, however, was not at all 

 seized with the importance of this discovery^ which be announced in two 

 lines of text, without giving a figure. It h, therefore, rather to Oustalet (18) 

 that the real honour belongs of investigating this point. His description and 

 figures are far in advance of any previous work on the subject, and mark a 

 very distinct step forward in the progi'ess of our knowledge. 



Following Oustalet, Chun (2) was the first to study the histology of the 

 rectum. He gives a figure purporting to show a transverse section of one of 

 the gill-lamellse of Lihellula depressa, Linn. But, as Sadones (25) has shown, 

 this figure is incorrect in very many details ; and, besides failing to recognize 

 the existence of the tracheal loops, established by Oustalet, it certainly does 

 not belong to the genus to which it is assigned by its author. In fact, it may 

 be stated definitely that no histological structure belonging to any known 

 Odonate gill-type can be found which at all corresponds with Chun's figure. 

 It is, indeed, very difficult to explain how his figure originated, except as the 

 product of an imagination rather more fertile than accurate. 



After Chun, Poletaiew (19) contributed a paper, which is of value in being 

 the first evidence of a disagreement with the generic determination of one of 

 the larvae studied by Dufour and Oustalet. This larva, which we now know 

 for certain to have belonged to the genus Anax, was called ^^schna by these 

 authors. Poletaiew, in examining undoubted larvae of the genus jEschna, 

 failed to find the papillae so carefully described by Oustalet. Hence, she 

 questions the accuracy of the descriptions of that author and of Dufour. 

 None of these authors seem to have attempted to breed out any of the larvae 

 which they were studying. The facts are, of course, well known to all 

 Odonatologists at the present time_, thanks to Ris (23), viz. that the gills of 

 Anax bear papillae, while those of ^schna do not. 



Amans (1), Roster (24), Faussek (8), E. Martin (16), and Dev/itz (4), have 

 all contributed to the study of the structure of the rectum and its tracheal 



