228 Description of a Species of Caligus. 
I. TrecumentTary System. 
a. Segments of the Body. 
The body of the Caligus is provided with a flexible, subcorne- 
ous, and perfectly transparent covering. By dissection, we were 
able to distinguish only two coats. The internal is a thin, moist 
membrane, easily separable from the exterior, and often present- 
ing, especially in old individuals, numerous dendritic delineations 
of an ochre-yellow color. Occasionally, they are so abundant as 
to give the animal an ochreous tinge. The exterior coat or shell 
is pellucid, very flexible, and somewhat elastic, and does not ex- 
hibit a fibrous structure. In some portions of the shell, and par- 
ticularly about the eyes, it is divided into areas, as represented in 
fig. 8, Pl. IV. The shaded subtransparent area in this figure 
passes longitudinally over the space between the eyes. 
When the animal dies, it assumes, after some time, a rose-red 
tint. Under the microscope, this color is found to be disposed in 
dendritic delineations, like the yellow color above noticed, and 
apparently in the same membrane with it; and in a few instances, 
we are confident that the dendrites which before were yellow, 
have this reddish hue. We cannot say that this is true of all 
these d ions. 
‘The body is composed of four distinct segments, (fig. 7,) of 
which the first two include the head and thorax, and the third 
and fourth, the abdomen. The anterior of these segments, which 
we may designate the cephalo-thoracic, is divided into four por- 
tions, by imperfect articulations. Two of these articulations are 
longitudinal, and separate the lateral portions of this segment from 
the central. The other articulation connects the centre of the 
two longitudinal articulations, like the cross-line in the letter H, 
and thus divides the central part of this segment into an anterior 
and posterior portion. The two lateral portions correspond to 
the united epimers of the higher crustacea, and may be called 
the epimeral segments; the anterior of the two central, may be 
called the cephalic sortion, and the posterior forms the anterior 
portion of the thorar. 'The anterior or cephalic segment presents 
an imperfect articulation near its front margin, which separates 4 
narrow segment; this segment we shall hereafter designate the . 
anterior or first cephalic segment, and the remaining portion the 
posterior, or second cephalic segment. 
a 
ae 3 
