284 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



It is not easy to figure the general appearance of a 

 fish containing these worms. The cysts are very opaque ; 

 the smaller ones being dead white in colour, the larger 

 faintly brown, and some are even dull red in life. In the 

 most highly infected specimens these cysts form a broad 

 band extending along the whole dorsal and ventral body 

 margins, widest about the middle of the body, and 

 tapering away towards each extremity. I counted over 

 160 such cysts in one plaice 2\ inches long. Some of 

 these cysts contained 10 parasites, and the average could 

 not be less than 5. This band marks the limits of the row 

 of axonosts supporting the fin. Internal or external to 

 this band few cysts are to be found, though occasionally 

 a few may be seen in the muscles of the trunk or in the 

 inter-radial tissues of the fins. The cysts are generally 

 long and narrow, and sometimes fused together. They 

 are present on both sides of the body, though, of course, 

 they are most easily seen on the blind side. 



Fig. 1 represents a section through the fin, in a 

 plane transverse to the long axis of the fish's body, and 

 passing through the interspace between two fin rays. On 

 the right side is seen most of a cyst containing 5 parasites, 

 and on the left is a complete cyst containing one parasite, 

 and beneath this part of another cyst. These structures 

 have been formed among the fibres of the muscles which 

 move the fin rays, as in the case of the cyst on the right 

 side in fig. 1, and as they grow the muscle fibres are 

 pushed aside or even partly aborted ; or, as in the case of 

 the cyst on the left side, they may be lodged in the tissues 

 between the muscles and the dermis. The cyst wall is 

 tough, and is made up of bundles of fibres pursuing a 

 straight or wavy course. Usually this fibrous wall may 

 be very dense, but at times it is loose and spongy. 

 Generally it is of no great thickness, but adjacent cyst 



