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BRITISH ENTOMOSTRACA. 
the animal to fix itself to its prey. Ledermuller describes 
them as antennae, and since his time, Dana and Herrick, 
and M. Edwards, have shown them to be the true antennae 
of the animal ; while, according to the latter author, the 
posterior pair of organs are the first pair of foot-jaws. 
The organs of the mouth are of a complex nature. The 
most prominent part is a long, sharp-pointed siphonal 
tube (t. XXXI, f. d , c). It arises at a considerable distance 
behind the antennae, and is formed of a very fine tube, in- 
closed in a flexible sheath. The extremity terminates in 
a very sharp point, at the top of which we see the orifice 
of a canal, hollowed out of the interior, which is prolonged 
to the commencement of the oesophagus. It is moveable, 
the animal being able to thrust it out rapidly from its 
sheath, carry it right or left, and project it far enough to 
reach the anterior edge of its shell. It can also cause it 
to enter into its sheath with the same rapidity by means 
of a slender muscle, which at one part is attached to the 
base of the sheath, and at the other to the middle of the 
trunk. The sheath is nothing but a prolongation of the lip, 
while the sharp-pointed portion constitutes the analogue 
of the mandible. Below the insertion of this siphon we 
see a convex, oval mass (f. d), containing the rest of the 
apparatus of the mouth. According to Dana and Herrick, 
who have described this part with great care, these con- 
sist of what is perhaps the inferior lip, and two pairs of 
maxillae in a rudimentary state. These authors consider 
that Jurine, who describes the convex, oval mass men- 
tioned above as the heart, is quite mistaken ; and that the 
motion which he considered the palpitation of the heart, 
is nothing but the rapid motion of the maxillae. 
The feet of the Argulus are generally described as of two 
different kinds : one used either for walking with or 
fixing itself upon its prey ; the other adapted for swimming 
when the animal is at large. What have been called the 
ambulatory legs are two pairs in number. They are the 
second and third pairs of foot-jaws. The anterior pair, or 
second pair of foot-jaws, (t. XXXI, f. e,f) is of a very 
