Description of a Species of Caligus. 257 



ed any blood in the stomach of these animals, although we have 

 often examined them, immediately on taking them from the fish. 

 On the contrary, the fluids always have a light color. 



We have not fully satisfied ourselves of the nature of its food, 

 but presume that it lives on the mucus which covers the body of 

 the fish. The mucus is one of the natural secretions of the fish, 

 and is always abundant. The organs of the mouth are well 

 formed for the collection of it, and the free motion in the whole 

 buccal mass seems peculiarly fitted for this purpose. 



Several specimens of the Caligus, when confined on their 

 backs in but a small portion of water, just sufficient to cover them, 

 have been observed to elevate the buccal mass, and take in glob- 

 ules of air, which passed down the esophagus into the stomach, 

 and thence through the intestine. Occasionally the globules of 

 air have been so numerous and taken in such rapid succession, as 

 to fill the stomach, and very much inflate it. In their passage 

 through the esophagus they usually stop for a short time at the 

 entrance to the stomach, indicating the existence of a valve or 

 sphincter at this place. 



b. Circulation. 



The blood of the Caligus, as in other Articulata, is a limpid 

 fluid, containing suspended in it numerous minute colorless par- 

 ticles. These particles are very various in their form and size. 

 The smallest scarcely equal 30V0 of ^^ inch. We have ob- 

 served one particle the length of which was about y| „ of an inch, 

 and its breadth ^ its length ; another had nearly the same length 

 and a breadth equal to J its length. These particles can accom- 

 modate themselves to the size of the passage through which the 

 blood is flowing, becoming narrow and elongated if the passage 

 is narrow, and again resuming their former proportions when they 

 have reached a free open space. 



The circulation in the Caligus is wholly lacunal ; it appears to 

 consist of broad irregular streams, passing through the spaces left 

 among the internal organs, and in no part have we discovered dis- 

 tinct vessels. These streams have in general definite directions, 

 yet are seldom uniform, continuous currents. They mostly ad- 

 vance by successive vibrations, depending on the palpitating action 

 of the body. A single centre of circulation, or a heart, this ani- 

 mal can scarcely be said to possess. There are two points in the 

 medial line where there is a valvular action, and each has its 



Vol. XXXIV.— No. 2. 33 



