PALMEN'S ORGAN AND ITS FUNCTION IN NYMPHS 



OF THE EPHEMERID/E, HEPTA'.IAIA INTER- 



PUNCTATA (SAY) AND ECDYURUS MACULI- 



PENNIS ( WALSH K 



J. E. \VODSEDALEK. 

 INTRODUCTORY RKMARKS. 



Our knowledge concerning the tracheal s\ ~u in in tin- Ephem- 

 eii-I.e .I. acs baclc to the time of Swammerdamm (1752 , luit the 

 existence of this interesting modification, Palmcn's or-an, found 

 only in the tracheal system of this group of insects, was not 

 knoun until comparatively recent times. Swammerdamm in his 

 "I'.iUI der N.itur" gives a large figure (Plate XIV. . -howin^ in 

 ome detail the internal anatomy of a may-tly nymph. Inn the 

 I'.ilmeii's organ and even the four tracheal tulu -. diivnlv leading 

 to it , if | in-sent in that species, apparently e>eaped his ob-en aiion. 

 Thi-> oini-sioii was no doubt due to an imperfeet di i < -lion ; for, 

 upon do-ely observing his representation of the air tul.es in the 

 he.id of the nymph he figures, one can detect .1 nnje projeetioii 

 le.idiiu fn>m the main tracheal tube on the left, \vhieh eorre-ponds 

 Mnne\\ h.it to one of the four tubes normally leading to \\\\< -n-.m ; 

 the other three tubes and the organ itself \\cre doubtle^> de- 

 Btroyed in his preparation, and hence not represented in his 

 figure. 



The presence of this chitinous structure \\.i- tir>t noted In 

 1 >r. J. A. I'.ilmen (1877), after whom the or^an is named, and in 

 his work he says: "Die vier im Schc-itel zusammenstossenden 

 Ae>te bildeii in ilirem Kreuzpunkt eincn rundliehen, aus c<m- 

 eentri^chen ( "hitinschichten besteheiiden Korper. dessen Medeut- 

 un.u iih nirht kenne." On Plate I. (Fig. 7) he gives .1 Imure of 

 the head and thorax of the nymph of Clocon diptcntni L., showing 

 tlu- loeat ion of this organ in its relation to the four traeheal tubes 

 of the head, without making any attempt to dexrilu- it. He 

 makes the statement that the tracheal >> stem is essentially the 



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