CALIGIDiE. 
265 
and provided with a duct which extends through the 
whole length of the thorax, and terminates, in the female, 
in the ovarian tubes; and in the male, in the genital 
organs, situated in the same place as the external ovaries 
in the female. They are thus analogous to the spermatic 
glands in the one, and the internal ovaries in the other 
sex. 
The abdomen is generally very small, in proportion to 
the rest of the body. It consists of only one joint, and 
sends off from its posterior edge two plates, each furnished 
with several pretty long plumose hairs or filaments. 
The intestinal canal may be easily traced through the 
parietes of the body, extending from the mouth through 
the length of the thorax and abdomen to the anus, which 
opens between the caudal appendages. It consists of 
an oesophagus, stomach, and intestine. The muscular 
system is well developed, and the muscles moving the 
different members may be easily traced through the pel- 
lucid skin. 
The circulation of the blood is fully described by 
Pickering and Dana. It seems to be wholly lacunal, 
and consists of broad, irregular streams, passing through 
the spaces left among the internal organs. No distinct 
vessels have been discovered. The number of pulsations 
has been found to vary from thirty to forty in a minute. 
The Caligi are only found upon marine fishes. They 
adhere to the body among the scales, by means of their 
foot-jaws, and can quit the place they have chosen, and 
move to another part of the fish. They are most fre- 
quently, perhaps, found on the parietes of the mouth and 
branchial cavities, but occur also indiscriminately on dif- 
ferent portions of the body. Sometimes they occur in 
great numbers, on the same fish. Pickering and Dana 
tell us that they are found most numerous on half-grown 
fishes, and that they have taken as many as forty specimens 
from one individual. On the salmon I have observed 
them in considerable numbers, and on various parts of 
the fish. We notice both sexes on the same fish, though 
