CALIGOIDEA. I343 



the apron, and enters them, and at the same time and place, passes in 

 part on the back ; the current from the apron flows laterally down 

 the abdomen. 



Another portion of the side-current leaves the buccal cavity just 

 alongside of the mouth, unites with A, and flows to the base of the 

 first pair of natatories. The union of these currents is somewhat 

 peculiar : the blood vibrates upward on the venter, to a spot near the 

 base of the prehensile legs, where a portion remains, although the 

 main current vibrates back on the venter ; at this moment, the cur- 

 rent comes from the buccal cavity and carries the whole below. 



The irregularity in the circulation in this animal is even greater 

 than will be inferred from the above description. These currents are 

 merely main directions; the blood flows into them or from them, 

 through all their extent. The current coming laterally down to the 

 base of the second pair of natatories, besides going into the natatory 

 and on the back, is carried up the venter at each of the upward vibra- 

 tions of the ventral current. The current from the apron also passes 

 into the same current, in addition to its backward course. When it is 

 considered that the currents of blood occupy merely the spaces left by 

 the muscles and other internal organs, it will be readily seen that 

 similar irregularities must occur in various parts of the body. These 

 directions are occasionally subject to singular deviations. One of the 

 two currents which run from each side in front and unite on the 

 medial line, has been observed to cross the medial line into the other 

 current, and thus continue flowing for some time with considerable 

 force ; soon after, each flowed by vibrations towards the centre, but 

 with alternate motion. This was observed immediately on taking 

 the Caligus from the water, when it was apparently very lively. As, 

 however, the cod from which they were taken, had been for several 

 days confined in the harbour near the market, all the specimens exa- 

 mined may have lost part of the activity usual in the open sea. At 

 times, the blood in some parts merely vibrates back and forward, 

 without advancing in either direction; and occasionally the blood 

 flows in a direction exactly the contrary to its usual course. 



We have not fully satisfied ourselves of the mode of respiration in 

 the Caligus. The natatory pinnulae — to which we must add those of 

 the tail, as they are identical in their structure — have been supposed 

 to supply the place of branchigs. When the animal is attached to 

 any object, these legs keep up a very regular action, which appears to 



