PALMEN S OKtiAN IN HKIMAt,! MA AND ECDYURl - 257 



with the layer surrounding the air tubes and apparently begins 

 active secretion at about the same time. The different con- 

 spicuous rings which are shown ( Fig?. 5-9) are sections through 

 the concentric layers of the organ and are directly correlated 

 with the various moults. Further evidence of this correlation 

 is obvious from the fact that the- number of rings is directly in 

 proportion to the size of the insects thcin-elves. An examination 

 of the sections figured show- thai tin- hypodermal cell- surround- 

 ing the organ are much larger than those enclosing the trachea-, 

 and hence, the greater the secretion <>f these larger cells; I nun this 

 results the greater thickness of tlu- chitinous layers of the on;. in 

 as compared with that of their continuations, tin- walls of the 

 t radical tubes. Coincident with tin- increase of volume of the 



in, the cells surrounding it must necessarily multiply as they 

 are pushed outward. Thus, by means of succe i\v periodic 

 BC< ret ions the Palmen's organ is built up; the old layers of the 



m arc not cast off as are the walls of the tradieal -y>tem, 

 \\ith which they are continuous. 



' .ross in commenting on the function of Palmcn'.-, or-an says: 

 "l>h glaube deshalb, dass fur das rath-elhafte < )r^an keine 

 KrlJarung gefunden werden kann oluie Beriicksichtigung de- 

 \ir\en. Xehmen wir aber an, dass dicker \\irklieh /.\\ dnn 



in gdiort, so kann dieses nichts anden-- >ein aU t in Sim 



m. Da es aber, wenn auch zicmlich direct miter der Ilypo- 

 di TinU von dieser nur durch wenig Feitk(")rper getrennt doch 

 jedeii 1 alls im Imiemdes Korpers der Thii n gelegen i-t. k.mn es 

 \ on alien uns %-on andern Thiergnippen bekannteii Sinne-func- 

 lionen nur denen eines Gleichgewichtssinnes dienen." I p to the 

 pn-si'iit study no experimental work on the ori;an has lui n at- 

 tempted with the view of obtaining evident--- ,nl- iis func- 

 lion. < '.ross also says: "Man konnte nieim-n. der Heueis fiir die 

 Kichti^keit der \ - on mir ver>uchten I'eutun^ (K-- < )r^an- \\> 

 sich \ idleicht durch zvveckmassig anuc-tellte X'ersudie i-rlirin^en. 

 1 >a- ei-M -heint mir aber ziemlich an icht>los. Es \\lire ja gewiss 

 nicht unmoglich, das recht oberll;ichlidi gelegene Organ zu zer- 

 storon, nachdem man vorher seine Lage so genau festgestellt hat, 

 ila-s man sie schon von an en am lelu-nden Thier angeben kann. 

 . \lier it h fiirchte, dieses Experiment wird nicht viel helfen. Stellt 



