INTERNAL ORGANS 167 



is a strong prejudice against eating these fishes on this account, 

 but the colouring is not due to any deleterious substance and 

 the flesh is wholesome and nutritious. 



The tissue clothing the skeleton, generally known as the meat 

 or flesh, is made up of muscles, and provides the greater part 

 of the bulk of the body. In the higher vertebrates the muscular 

 system is a compHcated one, but in the fishes the arrangement 

 is comparatively simple, and represents a primitive condition. 

 The most important muscles are the great lateral bands running 

 along the body in the trunk and tail — the muscles concerned 

 with the locomotor movements. In the ancestors of the fishes 

 these may have formed continuous bands running from the 

 head to the tail, but in all living forms they are divided trans- 

 versely into a series of segments, corresponding in number to 

 the vertebrae, each of which usually has roughly the shape of 

 an S. On either side each of these segments or myotomes is 

 further divided into an upper and lower half by a groove 

 running along the length of the fish. If the scales are removed 

 from the side of a fish a number of parallel white stripes of 

 zigzag form may be seen, representing the edges of the thin 

 partitions between the successive myotomes. In the neighbour- 

 hood of the fins the segments are variously modified for their 

 special duties, and in the head there is a more comphcated 

 system of muscles, each with its own particular task: one set 

 to move the eyes, another the gill-arches, another the jaws, and 

 so on. 



As a general rule, the muscles of a fish are white or pinkish 

 in colour, but in the members of the family which includes the 

 Tunnies {Thynnus) and Mackerels {Scomber) they are charged 

 with animal oils and appear deep red. The characteristic 

 colour of the flesh of the Salmon (Salmo), a beautiful orange-red, 

 is also due to the presence of certain oils. When a Salmon runs 

 up the river after a season of abundant feeding in the sea the 

 flesh is firm and red, and there is a good store of fat in the 

 tissues, but as the time for breeding approaches the fat is 

 expended on the development of the roe and the flesh becomes 

 pale and watery. Not only the colour but also the taste of the 

 flesh varies to some extent in diflferent fishes. The palatability 

 of a fish is due to the presence of some pecuhar chemical 

 substance in the muscles which gives it its characteristic flavour. 

 There is, for example, an immense difference in the flavour of a 

 Plaice {Pleuronectes) and a Sole [Solea), the latter being regarded 

 by many epicures as the most tasty of all fishes. The explanation 



