Description of the Argulus Catostomi. 303 



of reproduction. Two oval yellowish vesicles or poxiches, (Fig. 

 1. rr.) are situated in the tail on each side of these laminae.* 



The anal orifice is situated between the laminas at the base of the 

 caudal sinus: the faeces are conveyed through a duct lying along 

 the central line of the tail, and pass out on the lower side of the 

 laminae. 



The hrain is situated near the upper surface of the shell over the 

 sucker, and at its posterior extremity is composed of three connivent 

 elliptical masses, of which two are nearly longitudinal, and the ante- 

 rior transverse. The central portion between these elliptical mass- 

 es, is of a deep reddish black. From the brain, nerves are given 

 out, which proceed down the abdomen, and supply the natatory 

 legs; below, another nerve is visible, passing to each eye. 



Posterior to the oval mass, and within the body, are observed four 

 imbricated laminae, of which the three anterior are cordate. Long 

 slender cords appear to proceed from the sides of each lamina, and 

 extend into the natatory legs ; those from the ^rs^ lamina extending 

 to the first pair of natatories, &;c. These cords have much the ap- 

 pearance of muscles. No blood is seen circulating in them, though 

 it is very discernible, in a broad backward current over them. This 

 current appears to arise from beneath the imbricate laminae, and thus 

 renders it probable that they have some connection with the heart, 

 if they do not actually compose it. The blood is limpid, and holds 

 suspended numerous egg-shaped particles, (Fig. 8,) and is propelled 

 by distinct pulsations, which occur about once in a second. The 

 length of these particles is about 4 oVoth of an inch, and the greatest 

 breadth about f ths of the length. The current above referred to, 

 cannot be traced along the abdomen ; but in the tail there are dis- 

 tinctly apparent two parallel currents, which diverge at the base of 

 the terminating sinus, and curving around the transparent margin, re- 

 turn into the body. Numerous subordinate currents ramify through- 

 out the tail, dividing it into minute areolas. 



In an upper view of the animal, a strong current is observed above 

 the heart, proceeding towards the brain, (Fig. 9. r.) where branches 

 are given out to the antennae and eyes. The antennary current, af- 

 ter reaching the antennae, is soon lost in the surrounding parts of the 

 shell. Just below, however, on each side, appear minute branching 



* All the specimens we have seen (about thirty) have been provided with these 

 vesicles. It is possible that we have not seen any of the male sex. 



