' 
I 
i 
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ø ill 
i eninye EN re ns vi 
Fig. 25. The chitinous rod. 
306 
Ås mentioned above the outertube 
consists of five pieces of which two pairs 
are laterally situated (fig. 22 fg) while 
one piece is ventral (h).7) The ventral 
pieces (f) of the two lateral. pairs are 
peculiarly transformed: in front they 
are bow-shaped, posteriorly they are 
prolonged as two long chitin sticks; 
partly connected with them are the 
pieces of the second pair (9), which 
are narrower, and the chitin of which 
is constructed similar to the vane of 
a feather. These two pairs of chitin 
pieces build together the flanks of 
the outer tube. Near its posterior edge 
the bow-shaped part of f g is furnished 
with the above named bundle of five 
long hairs (4), and on its dorsal side 
we find the two long bristles (b). Above 
the real bore tube, the posterior part 
of the whole sipho, we find the above- 
mentioned two cushion-shaped pieces 
with the two long curved bristles (C). 
The tube is dorsally split; the long 
median plate (m), which belongs to the 
inner tube, can slide forward and back- 
ward in that furrow. This plate is furn- 
ished with a series of very hard saw- 
teeth. Ventrally the tube is closed by 
a lancet-shaped plate (h), the apex of 
which consists of more light-coloured 
chitin. The five chitin pieces mentioned 
above lie as dark-coloured lists within 
a tube of soft hyaline chitin carrying 
on its apex a number of sharp, dark thorns of chitin (k). 
The inner tube (fig. 25). As stated above, the two tracheal 
trunks are united to a common long tube, furnished anteriorly 
with a large bow-shaped curve, posteriorly with a number of ex- 
') In fig. 24 erroneously significated n: 
