168 



Appendices to Fourth Annual Report 



pale white muscles. The red fibres are arranged in series with the myo- 

 tomes. The red muscle is thickest along the lateral line, although it does 

 not follow this line exactly, and it shades off dorsally and ventrally. The 

 appearance of these red fibres is shown in Plate TV., fig. 1, in a 

 herring after being boiled. The exact distribution and thickness of this 

 muscle is better seen in a transverse section through the body, as is shown 

 in Plate V., fig. 1 R, being in front of the dorsal fin and behind the 

 anal fin. It will be observed to be crescentic in shape and thickest in 

 the interval between the dorsal and ventral portions of the myotomes, and 

 tapering away to become thinner as it passes dorsally and ventrally. The 

 tint of it is fairly well represented in the figure. A thin slip from it 

 passes inwards horizontally at each myotome, to be attached to the 

 vertebral column. As shown in Plate V., fig. 5, two thin red muscles 

 diverge from the middle line just at the base of the tail, to be inserted 

 into the fin rays. 



Whiting. — A similar arrangement of a segmented lamina of a coloured 

 or red muscle exists in the whiting, as shown in Plate lY., fig. 2, 

 but when boiled the colour passes more into the yellow. It does not 

 form, however, quite so continuous a layer as in the mackerel, being 

 thickest over the centre of each myotome and thinner opposite the con- 

 nective tissue septa. In transverse section its distribution is shown in 

 Plate v., figs. 3, 4. In these figures it is thickest just under the 

 position of the lateral line and between the dorsal and ventral parts of 

 the myotomes, being wedge-shaped in section (R). Prom this wedge-shaped 

 part, as seen in section, fibres directed longitudinally pass down to the 

 vertebral column. Two other thin wedge-shaped parts exist in the intervals 

 between adjoining cones of the myotomes, one above, R' and one below, R' 

 on each side, and some prolongations of these pass inwards to reach the 

 middle line. Some coloured fibres exist in connection with the dorsal fins. 



Mackerel. — A similar red muscle exists in the mackerel, where, how- 

 ever, it is deeper tinted and more highly developed, as is shown in Plate 

 v., fig. 9. In fig. 10 its crescenting shape and continuation inwards 

 on both sides as a well-marked horizontal prolongation of muscular sub- 

 stance attached to the vertebral column. The red muscle is so strongly 

 marked that it at once arrests the attention when a transverse section of 

 the body of the aniuial is made. 



Haddock. — An arrangement similar^to that in the haddock exists in this 

 fish, the lighter yellow of the boiled red muscle being shown in Plate 

 IV., fig. 6. There is the corresponding radiating muscle attached to 

 the rays of the tail. 



Similar red muscles exist in many fishes, e.g., the salmon, and many 

 others ; and as soon as time and opportunity occur it is my intention to 

 investigate further the distribution and arrangement of these red muscles 

 in fishes generally. 



In flat fish, such as the plaice^ the red muscle is well developed, as 

 shown in Plate III., where the light brown tint of these muscles 

 after boiling is shown. The fishes were all boiled to enable the skin to 

 be readily removed. It will be seen to follow the zig-zag course of the 

 myotomes, being thickest along the mesial lateral line, and thinner as it 

 goes outwards ; while it is thickest over the centre of each myotome, and. 

 thinner over the septa of connective tissue. A thin separate red muscle, 

 blended with or rather lying in a depression of a white one, is to be seen 

 along the marginal fin rays. The latter appear most distinctly when the 

 fish is skinned and left exposed to the air for a time, when the pigment, 

 even though altered by boiling, assumes a deeper tint. In other flat fish; 

 such as the flounder, a similar red muscle exists. 



