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tremely hard prolonged chitin pieces; the median dorsal piece is 
furnished with numerous saw-teeth; the two lateral pieces carry 
two thick, outward curving thorns on the apex (0). Ventrally to the 
point of union of the two tracheal trunks a long straight chitin 
staff is placed (p) reaching nearly to the middle of the eighth seg- 
ment. The staff is flattened, black, dilatated into a broad plate of 
EM 
Fig. 26 a, b, c. Sagittal sections through the sipho. 
lighter chitin at the anterior end. A series of sagittal cuts (fig. 
26) through the sipho shows (fig. 26 5), that the staff is hollow, its 
lumen communicating with that of the tracheæ. The inner side 
of the common trunk of the two tracheæ is equipped by a coarse 
hair felt beginning near the point where the trunk is covered with 
chitin pieces. i. e. where the trunk is used as a piercing organ; 
anteriorly the hair felt reaches the point of union of the two 
tracheæ. Fig. 27 represents a series of horizontal sections. In a 
the chitin staff (p) and the lumen of the tracheal trunk (e2) have 
just been hit. The section b represents a cut through the whole of 
the lumen of the united tracheæ; the figure shows, that the trachea 
terminates with a single orifice surrounded by chitin pieces. In 
Cc the cut has reached the bottom of the inner tube. In d the 
Cut has passed almost entirely outside the piercing tube and met 
with the edge of the broad part of the sipho. The cut e has had 
another direction, exhibiting the point where the two tracheæ de- 
bouch into the large common trachea; its lumen may be regarded 
