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as a large air-chamber; the hatching indicates the felt cover of 
the walls. 
The transverse sections fig. 28 a—j give the same picture of 
Fig. 28, Series of fransversal sections through the sipho. 
insertion in the 8th segment; we see the two tracheæ and the 
chitin staff (p). In b the common trachea (e2) has been cut at 
the point where it coalesces with the chitin staff (p). Section c 
is cut through the bow-shaped chitin piece f near the point of 
Origin of the piercing part of the sipho. The following transversal 
Sections d—j have been cut through this part, e just at its origin. 
In section e the two lateral pieces f and g of the outer tube are 
