CALIGID^. 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 generall}' 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 nuiscular 

 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 lacuna!, 

 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 



