BY R. J. TILLY A RD. 35 



that T can find as to their supposed respiratory function seems 

 to have been thrown out by Cams (7), who, while describing the 

 blood-circulation in these organs in the larva of an Agrionid, 

 applied, amongst othei* terms, the name yill-likf Imjit'ts ("kiemen- 

 artigen Blattchen") to them. This may, or may not, have con- 

 veyed a hint that he thought of them as possible gills. Some 

 twenty-five years later, we find Dufour(9, 10) and Hagen(12) 

 using names for them which show us that they accepted theii- 

 respiratory function without question. The former^ — to whom, 

 by the way, we must credit undoubtedly the first discovery of 

 rectal folds, with a possible respiratory function, in the larva? of 

 Caloptpryx — termed the lamellar appendages of Aijrionid larva? 

 external or caudal gills ("branchies exterieures ou caudales"), 

 adding (in agreement with Reaumur) that they were also in the 

 nature oi Jins. This author's disagreement with the observation 

 of Reaumur on the question of the position of the spiracles is 

 well-known, and the fact that we now know that Reaumur was 

 completely in the right does not add to our confidence in Dufour's 

 capacity for judgment, Hagen, who accepted Dufour's deter- 

 mination of the rectal folds in Calo'pteryx larva? as gills, speaks 

 of the lamellar appendages of Agr'umid larva? as fail-gills or 

 caudal gills ("8chwanzkiemen"), the name which appears to 

 have remained in common use ever since. 



It would be out of place here to attempt to give a complete 

 list of the authors who have used the term caudal gills for these 

 organs since Hagen first invented it. It seems to have come 

 into general use, not only in scientific treatises, but also in text- 

 books, encyclopjedias, and works of a jDopular nature. The 

 reason for this ready acceptance would appear to be the form of 

 the organs themselves, in which the richly-branching trache?e at 

 once suggest a respiratory function. We must note, however, 

 the observations which appeared from time to time as to the 

 well-known ability of Agrionid larvie to live without their caudal 

 gills. Such observations may be found in von Rosenhof (30), 

 Hagen (12), Sharp (35), Tillyard(37) and others. Taken together, 

 they amount to a growing recognition that the caudal gills 

 could not possibly be the only organs of respiration for Zygop- 



