228 Description of a Species of Caligus. 



I. Tegumentaky System. 



a. Segments of the Body. 



The body of the CaUgus 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, PI. TV. 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 delineations. 



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 epimerae of the higher Crustacea, and may be called 

 the epimeral segments ; the anterior of the two central, may be 

 called the cephalic portion, and the posterior forms the anterior 

 portion of the thorax. The anterior or cephalic segment presents 

 an imperfect articulation near its front margin, wliich separates a 

 narrow segment ; this segment we shall hereafter designate the 

 anterior or first cephalic segment, and the remaining portion the 

 posterior, or second cephalic segment. 



