LERNEADiE. 
317 
thorax. This latter is generally of considerable size, whilst 
the abdomen, in almost all the species, has become very 
nearly rudimentary. Attached to the head, in the greater 
number of the Lerneadse, we find one pair of antennae, 
and two pairs of foot-jaws, by means of which they attach 
themselves to their prey. In a few we find no antennae, 
and only one pair of foot-jaws. We find no appearance 
of eyes. The organs corresponding to the thoracic feet 
of the Siphonostoma are variable in form, but in general 
are almost rudimentary, sometimes, indeed, altogether 
wanting. It is this very rudimentary state of the organs 
of motion and other appendages that forms the principal 
mark of distinction between the Lerneadae and the Sipho- 
nostoma. The mouth, according toKroyer, has generally 
the shape of a blunt, spherical snout, placed on the most 
advanced portion of the head, and terminating in a 
roundish opening, though in some of the genera it is in 
the form of a slight elevation merely, and is placed at 
a considerable distance from the anterior part of the 
head. 
The manner in which these animals fasten themselves 
to the fishes upon which they live varies much. In some, 
it is by means of the foot-jaws alone, which in these 
species are strong, and of a hooked form. In others, it 
is by means of two long appendages springing from the 
upper part of the thorax, one on each side, and uniting 
at the tip, forming at their junction a sort of round 
button. In a third set, again, the organs of attachment 
are a series of horns or appendages proceeding from the 
side of the head. 
The females are generally furnished with large external 
ovaries, containing numerous ova. The intestinal canal 
is very distinct, extending through the whole body. It 
is cylindrical, and widens towards the middle of its length 
into a stomach. The motion in the living [individuals 
may be plainly seen, a series of rhythmical movements to 
both sides, occurring to the number of from about sixty 
to sixty-five in the minute ; besides a sort of peristaltic 
