304 Description of the Argulus Catostomi. 



vessels, in which the blood has a returning course. These minute 

 vessels discharge themselves in a broad channel, (Fig. 9. n.) which 

 enters the body near the base of the abdomen. 



The ophthalmic current, which is most distinctly seen in an under 

 view, curves at the eye and passes backward, enters the suction legs, 

 is seen again between those legs and the prehensile, and also for a 

 short distance posterior to the latter, after which it disappears. 



Another current (Fig. 9. k.) goes out laterally, a short distance be- 

 hind the brain, to the anterior margin of the reniform area before 

 described. It passes just within the exterior margin of the same 

 area, and returns into the body after a final course along the inner 

 edee of each lobe of the shell. 



Near the base of the abdomen arises a fourth current, which run- 

 ning downward and outward is diffused through the lower portions 

 of the shell, and probably returns into the body by the same cur- 

 rent with the preceding. 



It is impossible to trace the passage of the blood into the bran- 

 chial legs. It is probable that the above currents, after returning 

 to the body, pass to these legs for aeration, and thence to the heart 

 to be again diffused throughout the animal. Pulsation is frequently 

 observable along the whole abdomen, and often with great distinct- 

 ness in the tail. The currents of blood are not apparently confined 

 within vessels of definite limits. 



The pairs of muscles by which the animal moves the various parts 

 of the shell are four. The Jirst, or that acting on the clypeus, arises 

 each side of the brain and accompanies the antennary blood vessels. 

 The second (oo) arises just below the base of the preceding, and is di- 

 rected outward and upward. Between this and the third is a suture, 

 which is apparent when either muscle is in action. The third ac- 

 companies the current of blood (k) which passes to the anterior part of 

 the reniform area. The fourth accompanies the current (m) which 

 flows to the posterior portion of the shell, and is attached near the 

 central part of this portion. Several of these muscles are easily 

 mistaken for the courses of the blood. The muscles of the legs are 

 for the most part visible, and are given in the plate. Two muscles 

 extend from their insertion, near the base of the prehensile legs, on 

 each side of the abdomen, and appear to cross near its extremity. 



The entire abdominal region below of the gravid female, is occu'^ 

 pied by eggs. The number of eggs which may be laid by one fe- 

 male, cannot be stated with certainty. On the 18th of June, 1836, 



