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Arffcis persicns 
wall of the sac and bulge out into the lumen. As mentioned in the 
previous section, the excretory products derived from the alimentary 
canal do not enter the rectal sac until the final stages of digestion are 
reached and in consequence the contents, as usually seen, consist 
entirely of the secretion of the Maljjighian tubules. 
The Malpighian tubules. 
Plates XIV, XV and XVI, t. mpg .; Plate XVII, fig. 7. 
These structures, two in number, enter the rectal sac on its ventral 
side, close to the median line, on either side of the rectal aperture (see 
PI. XV, 0 . t. mpg.). 
In appearance, the tubules are opaque creamy-white, the colour 
being due to the contents, as was seen to be the case with the rectal 
sac. They are generally slightly flattened in cross-section, unless 
distended with secretion, and their diameter varies somewhat in different 
parts, the average diameter being about OT mm. 
The Malpighian tubules follow a somewhat complex course through 
the body of the tick and extend almost to the anterior end of the body. 
From their point of origin at the rectal sac, the two tubules run for a 
short distance backwards, each following the lateral contour of the rectal 
sac. Before reaching the posterior margin of the latter, however, they 
suddenly turn forwards and upwards, passing through the deep notch 
between the two subdivisions of the postero-lateral lobes of the stomach, 
and emerge on the dorsal surface of the gut. After crossing the neck 
of the postero-lateral lobe, the tubules return to the ventral part of 
the body cavity once more, passing downwards through the notch which 
separates the antero-lateral and postero-lateral lobes of the stomach. 
From this point they continue their forward course for a short distance 
alongside the genital canals in the adult, and then turn outwards 
beneath the salivary glands, along the lateral margins of which they run 
towards the anterior end of the body, where they terminate blindly at 
the level of the basis capituli, the blind extremities being situated, as a 
rule, in or near the camerostomal folds. 
The Malpighian tubules are occasionally coiled and reflexed on 
themselves, but not to nearly the same extent as those of the Ixodid 
ticks, in which, though the general arrangement is similar to that 
described above, the whole system is complicated by the numerous 
secondary convolutions which they exhibit. On account of the non¬ 
development of the.se secondary convolutions, the Malpighian tubules of 
