anterior part without detaching it. The anterior part, 
when thus separated from the posterior, retains its vital 
powers for at least twenty-four hours. At first it swims 
about vigorously, but after some hours begins to get 
sluggish in its movements, and then finally dies. The 
posterior part does not live long when separated from the 
anterior. The parasites can be kept alive in sea water for 
upwards of six weeks after removal from the fish. 
EXTERNAL CHARACTERS. 
The animal is depressed dorso-ventrally, and is of a 
more or less oval shape, and distinctly divided into four 
parts (Plate I., fig. 1). The foremost one of these parts, 
and usually the largest, is almost circular in outline, and 
has all the appendages, with the exception of the fourth 
and fifth pairs of feet, attached to it. This part is known 
as the cephalo-thorax. 
Viewed from above, this region is seen to be slightly 
convex and divided into four portions by imperfect 
sutures. Two of these sutures are longitudinal, and 
separate the lateral parts of the region from the central. 
The remaining suture joins the centre of the two longi- 
tudinal sutures like the cross line of the letter H, dividing 
the centre of the cephalo-thorax into an anterior and a 
posterior portion, of which the anterior is the greater. 
There is also an apparent suture near the frontal margin. 
The frontal margin is indented, the greatest depth being 
in the middle line. This indentation to some extent is due 
to the sear caused by the breaking away of the filament 
for attachment in the “chalimus” stage. In the centre 
of the hollow, situated on the ventral surface, is an oval- 
shaped opening (6) with a chitinous fringe. This ts 
evidently a sucker, and represents the remains of a median 
sucker which is considerably developed during the * chali- 
