ORIGINAL COMMUNICATIONS. 
Nete on an Unpiscrisep Species of Acarus, found in 
the Picron, Columba livia. By Cuartres Rosertson, 
Demonstrator of Anatomy, Oxford. 
(Communicated to the Oxford Microscopical Society, Feb. 15, 1866.) 
Tue parasites which I shall briefly describe are small, oval, 
white, maggot-like animals, distinctly visible to the naked 
eye, and are found chiefly amongst the connective-tissue of 
the skin, the large veins near the heart, and on the surface of 
the pericardium. When few are found they generally adhere 
closely to the surface of the pericardium, and to the large veins 
near the heart. If the veins have been previously injected 
with size and vermilion, the white transparent acari are 
seen very distinctly on their red delicate walls. All the 
examples which I have examined were very transparent 
without any trace of well-defined digestive or generative 
organs, even when examined with the highest powers. 
The body does not generally present any trace of constric- 
tions, but in a few examples I have observed one or two faint 
lines, giving the body a segmented appearance, but this may 
be caused by a mere folding of the soft cuticle. On the ante- 
rior and inferior surface of the body a ridge extends inwards 
and downwards from the base of the anterior pair of legs, and 
unites with a median single backward ridge. A similar ridge 
runs in the same direction from the base of the second pair 
of legs; but instead of meeting, as in the first pair in the 
median line, are united by a transverse ridge, and a similar 
ridge is continued backwards from the points where this line 
joins those from the limbs. This arrangement reminds one 
of the head of the larva of a hexapod insect. No trace of 
palpi, mandibles, or suckers could be found. Four pairs of 
short, jointed legs were found in all the specimens examined ; 
the two anterior pairs are placed close together, on the ante- 
rior and outer extremity of the body ; the two posterior pairs 
have a considerable interval between them and the anterior 
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