60 



Part III. — Twenty -eighth Annual Report 



In general appearance the fishes were well nourished and normal,except 

 that they were thickly covered all over the body and fins with black dots. 

 Under the lens, each black dot was seen to be a little oval translucent cyst 

 surrounded by an irregular ring of black pigment. They are shown enlarged 

 in fig. 30, where they appear shining through the scales. 



In a section of the skin it is seen that the cyst occupies the whole 

 thickness (fig. 33). It rests inferiorly on the layer of fascia (I. I.) between 

 the skin and the muscles. It reaches above into the lower surface of the 

 scale- pit (scp.). The epidermis is not shown in the drawing. Some of the 

 cysts reach the surface in the inner part of the scale-pit, in which case they 

 are, although surrounded by pigment, not visible from the outside. 



The cyst measured "35 x *3 mm. and the oval body within was '22 x *2 

 mm. in size. When the cyst was dissected out of the skin it was found to 

 be very tightly bound to the fibres (fig. 32), and these fibres formed a zone 

 round the body ; they did not cover its whole surface. 



The trematode character of the larva was evident. The skin was longi- 

 tudinally and transversely grooved. I was not able to make out any 

 spinules on the skin. The cyst had two investments, the outer a thick rind, 

 the inner a thin membrane closely applied to the larva. 



The cysts were found also in the cornea, on the eyeball within the orbit, 

 on the inside surface of the mouth, and some were sunk in the muscles of 

 the dorsum, and head. They were revealed by the black pigment 

 accompanying them. In the eye, some cysts which were lodged in the 

 gelatinous matter between the cornea and the lens had no pigment. 



A large number of cysts were found within the brain cavity, in the spinal 

 canal, and in several spinal nerves. The nerves were distended at the 

 points where the cysts were located. There was no black pigment associated 

 with these. None were observed in the tissue of the brain or of the spinal 

 column. Two cysts from the auditory organ measured 1 x '5 mm. and 

 *55 x '4 mm. Four empty capsules were observed in the same organ. A 

 cyst was found between the muscles and the top of the skull. It measured 

 •7 X -57 mm. 



The cysts found in the nerves, measuring -6x'4 mm. and 55 x "35 mm. 

 in size, contained larvae that resembled exactly those of G ' aster ostomum 

 gracilescens as figured by Lebour* {Plate I., figs. 2 and 3). They were 

 larger than those in the skin, and contained young forms of a more ad- 

 vanced stage. The cyst had a double-layered investment. The larva 

 exhibited a different appearance in its integument according as it was 

 extended or contracted. In the latter case the rugae were very prominent. 

 Anteriorly the surface of the skin exhibited a net- work appearance. At the 

 edge, the body appeared serrate and the backward directed teeth described 

 by Johnstonef were made out. Posteriorly, wh^e the faint transverse 

 grooving was evident, no spinules were made out. In surface view the net 

 markings on the anterior end were accompanied by comb-like structures 

 which may have been groups of teeth. When the trematode is extended it 

 is very difficult to make out the above-mentioned structures. The teeth 

 were not definitely seen in that condition of the worm. 



The pigment which surrounds the cyst does not apparently belong to it, 

 because in certain regions the pigment was absent. The presence of the 

 parasite would seem to stimulate the development of pigment in the 

 surrounding tissue. 



Four spotted whitings, measuring in one case 31 cm., were examined in 

 February. The embryo parasites did not seem to be any further on than 

 those described above. Four others were obtained in March. Of these, one 



* Lebour : "Fish Trematodes of the Northumberland Coast." Northumberland 

 Sea-Fisheries Report for 1907. 



f " Johnstone : Internal Parasites and Diseased Conditions in Fishes." Trails. 

 Biol. Socy., Liverpool, Vol. xix., 1905, p. 98. 



