Structure and Life-history of the Holly-fly. 269 
consists of an air-containing cylinder (‘felted chamber”) 
which, arising from the end of the tracheal extension, runs 
up the stalk and terminates in an expanded “ end-plate.” 
The closed spiracle is attached to the side-wall of the 
stalk and connected by a solid cord (“ Narbenstrang”) with 
the end of the tracheal extension. The cavity of the air- 
containing cylinder is subdivided by chitinous trabeculz 
into minute spaces, and presents a dotted appearance when 
the air has been removed by alcohol. The end of the 
tracheal extension has the same structure. The end-plate 
of the spiracle is flattened from side to side, and carries 
on its inner and posterior faces six or more radiating pits 
(the number is not constant). Each pit has a thickened 
KW 
Fic. 9. 
Posterior spiracle of larva of 3rd stage. 
Lettering as in fig. 8. (x 330.) 
margin from which an oval appendage hangs down like an 
earring in the space outside the air-containing cylinder. 
From each appendage a delicate filament is given off, 
which, passing down the stalk, branches and ends in 
intricate beaded coils, resembling the termination of a 
nerve on a muscle-fibre. The structure of the posterior 
spiracles (tig. 9) is similar to that of the anterior ones, the 
felted chamber, pits, appendages and filaments, and the 
closed spiracle being all present. The pits are more 
elaborate, and resemble miniature spiracles; they are 
carried on prominences which are situated on the outer 
side of the end-plate, and vary in number from five to nine, 
the number being usually different in the two spiracles, 
Each pit apparently opens to the exterior by a slit. 
