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the ventral, and the outline of the body is an oval with projecting ends, so that its 

 shape resembles that of a small leaf. The animal, when adult, is usually about one- 

 fourth of an inch in length (6 or 7 mm.), and one-eighth of an inch (3 mm.), in 

 greatest breadth, but young individuals are smaller, and larger specimens are often 

 seen. The structure of this parasite is shown in the accompanying woodcut, Fig. D, 

 which represents the appearance of a living specimen under the microscope. At the 

 posterior end of the body is a large muscular sucker, p. s., almost circular in shape : 

 the concavity of this sucker is ventral, and it is attached to the body by a peduncle 

 at about the middle of its dorsal surface. On the ventral side of the sucker are two 

 pairs of hooks imbedded in the skin, with their recurved points protruding. One 

 pair of these hooks are long and directed backwards, their points being near the 

 posterior edge of the sucker, the other pair are short, and their points near the centre 

 of the sucker. At the anterior end of the body there is a semicircular projection, the 

 ventral edges of which are provided with a pair of glands, a.g., for adhesion Behind 

 this projection is the small mouth, and at the left hand side of the projection are the 

 two genital apertures, p., u., close together. The worm crawls about on the skin of 

 the lower side of the sole, anchoring itself to the spines of the fish's scales by means 

 of its sucker and its hooks, and using the anterior glands for adhering by that end 

 when it moves its posterior sucker from one position to another. 



The most extensive and conspicuous organs are the generative, male and female, 

 for the animal is hermaphrodite, arid each individual produces both spermatozoa and 

 ova. The digestive organs are small, consisting only of a sac-like organ into which 

 the mouth opens, and which is lined by very large cells with enormous nuclei. This 

 organ may be called the alimentary sac, since it presents no distinction of parts. In 

 front of the alimentary sac dorsally are two simple nerve ganglia, giving off a main 

 lateral nerve cord on each side, which passes backwards. In the skin above these 

 ganglia, the cerebral ganglia, are two pairs of eyes, or rather pigment spots which 

 are doubtless organs sensitive to light. The renal organs consist of a system of minute 

 ramified ciliated tubes communicating with two main lateral tubes, which probably 

 open by a single dorsal opening at the posterior end. The rest of the body consists 

 of the generative organs, and a dense parenchyma of cells filling up the interspaces 

 between the various organs. 



Uniformly scattered throughout the parenchyma of the body are a large number of 

 globular organs consisting of aggregations of peculiar cells : these are the yolk-glands. 

 They are situated at the ends of the ultimate ramifications of a ramified system of tubes 

 which are the yolk-ducts, and which are completely filled with granular gtobules similar 

 to the contents of the cells of the yolk-glands. The yolk-ducts on each side of the body 

 ultimately unite into a single large duct which opens into a sac situated a little to the 

 left of the middle line, about one-third of the length of the body from the anterior 

 end. This is the yolk-reservoir : it is elliptical in shape and transversely placed. The 

 yolk-reservoir is filled with the same material as the yolk-ducts ; the terminal yolk-ducts 



