262 
BRITISH ENTOMOSTRACA. 
eyes of the animal. Later authors have proved this 
opinion to be erroneous, and Pickering and Dana consider 
them as true sucking-discs, by which the Caligi attach 
themselves to the fishes upon which they live. They 
assert, in proof of the correctness of this opinion, that they 
have frequently tested the use of these organs by apply- 
ing the blade of a knife to the inferior surface of the front 
margin, while the animal was on its back, and that in 
numerous instances it adhered so firmly to the knife, that 
it was lifted up and carried to some distance. It exists, 
however, only in some of the species, and its presence 
or absence has been used by Nordmann as a generic 
character. 
The eyes are two in number, and are situated nearly in 
the centre of the cephalic segment. They are small, 
simple in structure, of an oval shape, and placed close to 
each other. In the living animal they are of a red colour, 
and are slightly projecting. 
The mouth (t. XXXIV, f. 5 /) is situated in the median 
portion of this segment, the eyes being placed directly 
over part of it. As in the Argulus, this organ consists 
of a siphon, or conical sucking-tube, composed of two 
long, slender, styliform organs, curved inwards, and armed 
on their points with about twelve teeth. These represent 
the mandibles, and they are inclosed in a sort of sheath, 
formed from the union of the parts corresponding to the 
upper and lower lip. Situated upon the sides of the 
sucking-tube we perceive two pairs of rudimentary ap- 
pendages (t. XXXIV, f. 5 d). The one, rising in front of 
the other, consists of a small basilar joint, terminated by 
a short, curved apex ; The other is more developed, and 
is divided into two stout, terminating claws, directed 
downwards. These constitute the analogues of the two 
pairs of jaws in the other orders of Crustacea.* 
* For a fuller exposition of this subject, see the very interesting memoir 
of M. Edwards upon the Organization of the Mouth of the Siphonostoma, 
as exemplified by him in the Pandarus alatus , in the ‘Ann. des Sc. Nat.,’ 
xxviii, 78 . 
