PALMEN S ORGAN IN HEPTAG1-.NIA AND ECDYURUS. 255 



and arrangement of the more important parts of the system were 

 carefully noted and a diagram indicating the relative position of 

 the main tubes was sketched. The external covering was care- 

 fully broken between the pro- and mesothorax and a gentle pull 

 on the anterior edge of the head removed it, fully exposing the 

 air tubes which remained in position. The macerated mass was 

 carefully washed off and the tracheal system being completely 

 filled with air presented the most beautiful silvery effect a-ain-t 

 a dark back-ground. Even the very finest branches remained, 

 but no attempt was made to include them in the figure. 



DESCRIPTION OF PALMEN'S ORGAN. 



Gross (1903) attempts to describe the organ in c<>n-i(lcr,il >! 

 detail; this description and his ideas in general an IK-I fully 

 corroborated by the results of my studies. He says in part: 

 " Reconstruiren wir jetzt aus den besprocheaen Schnittbildern 

 ganze Organ, so erhalten wir folgendes Gesammtbild, Kin 

 K'irper, der im Liingsschnitt kurz elliptisch, im < >IKT chnii i 

 ungerfahr kreisfdrmig ist, setzt sich aus 14 concentrischen, an- 

 xaitem Chitin bestehenclen Schalen /u-ammm, die an ilnvr 

 Innentluche mit feinen Hiirchcn dicht U--rut -iml. I >as Kllip- 

 s<>il i-t aberkein vollkommen geschlosseiie-. Yielmehr i-t es v>n 

 vier Seiten her [sehr] tief ausgehdhlt. Das uan/c i-t in den Kn-n/- 

 nn^-punkt von 4 im Scheitel des Hinterkopfs /n-ainmm'ivtti-n- 

 dm Tracheeniistcn eingeschaltet, und xuar so, da-.- die Luft 

 /\\i-elien den Schalen trei circuliren kann, \veiin aiich (lurch <li<- 

 grosse Xahl der Hiirchen einigermaassen behindi-rt. < ".an/ ahn- 

 lich i^estaltct wie bei Ephemera vulyitd L. fand irh da- I'alinm'- 

 selie ( )r^an noch bci Baetis rhodani Piet.. Ht'()ttr^cnia sulphured 

 Miill.. ferner bei den Larvcn einer Cacnis sp. un<l eiiur Chiro- 

 les sp. Einige geringe Abweirhnn-en in di-r Cn--talt bei 

 />'<.-(V/.v rhodani konnte ich nicht hinreii IK-IK 1 ^ciiau fe-istellen, 

 nn -it- hier zu besprechen, da ich inir nieht lienii^md Material 

 1'. ~i haticii konnte." 



The 1'almen's organ in both II. inter punctata and E. niacnli- 

 f>cnnis, i- not composed of coneentrie shells nor are there any 

 hair- pp sent on the inner surface of the scales which Gross 

 Ic-cribes and pictures in allied -prcie-. \\V11 prcparc'l -tides 



