Report on Diseases and Abnormalities in Fishes. 7 



Is the thallus formed independently of the larva? Does the 

 larva merely feed upon the thallus ? Or does the thallus grow on to 

 the larva? Might the thallus be derived from the breaking up of the 

 blood ? Is a part of the columnar body analogous to the thallus ? 



The following appears to be the description of the parasite : — 

 The larval parasite enters a capillary blood vessel and lodges 

 there. It grows larger and, as it does so, it pushes out the wall 

 of the capillary in a series of pouches for the accommodation of 

 its increasing bulk (pa., fig. 13). At the point where the capillary is 

 blocked by the parasite the vessel is distended to form a blood cyst 

 (s.) The branches of the parasite eventually separate off and wander 

 as elongated larvse further along the capillary, following its branches. 

 The larva was not observed to move, and it is probably forced along 

 the capillary by the propelling action of the heart. It then assumes 

 a spherical form, thereby no doubt blocking the capillary (fig. 175). 

 This encysted form seems to grow into a columnar bod} 7 . The 

 capillaries occupied b} 7 the parasite are filled with a translucent fluid 

 (serum). The part of the vessel occupied by the parasite becomes 

 surrounded by a thick development of connective tissue. 



In the stages described above I observed no spore-formation. The 

 form cannot therefore be definitely regarded as a sporozoan. It 

 shows, however, some points of resemblance to stages in certain 

 Myxo-sporidia. Bertram's drawing * of the cyst of Sarcocystis tenella, 

 found in the muscle of the sheep, has a general resemblance to the 

 cyst in jbhe spotted haddock. The plate of figures of PfeifFer's 

 Myxobolus sp.t also recalls in some respects the present parasite. But 

 the former is said to penetrate the muscle cell. Johnstone's drawings 

 of a fungus found in the viscera, kidnej 7 , and mesenteries of the 

 plaice resemble certain portions of this parasite. 



I have regarded this parasite- as undescribed, and I propose the 

 name Dokus adus for it. 



Diseases in Cod (Gadus callarias). 



Green Parasite (Roles trelis, n. sp.). — The muscles were green- 

 coloured, as if with a dye, at one part. The stained portion was in the 

 muscles resting on the dorsal side of the lateral processes of the verte- 

 brae. It measured 1 inch (2 - 5 cm.) in length hy 1-inch (1 cm.) in 

 breadth. Figs. 65 and 76 show sections of the region. A broad line of 

 dark green (1.) crosses the muscle. It seems to run along an aponeu- 

 rosis. The muscles on either side are stained green (shown shaded in 

 the figure). The stain extends well all round and gradually gets 

 fainter as it recedes from the central line. Along the central part the 

 parasite consists of dark green bodies. Little brown bodies are seen 

 scattered through the muscles in the fringe of the greenish area. 

 There is another centre (p.) with little elongated bodies of a dark 

 green colour, and outside them other bodies brown in colour. The 

 brown bodies are in the connective tissue between the muscle fibres. 



The muscle fibres did not appear to be stained nor affected by the 

 parasite. The connective tissue is increased in quantity round the 

 parasite, and it appears to be stained. 



Fig. 64 is a drawing of a small part of the parasite. A number of 



* Vide Braun. t Vide Gurley. 



