194 ANIMAL LIFE AND HUMAN PROGEESS 



the following analysis,^ and may be contrasted with the 

 composition of the cod : — 



Fat 



Proteid 



Ash ( + salt) .... 



Water (+ traces) . . . . 48 81-7 



Other Manx herring, however, caught in September 1917, 

 cured in brine and analysed in winter, gave as much as 

 32-72 per cent of oil (fat). 



It is this relatively large amount of easily digestible fat 

 in the flesh of the herring that gives this fish its special value 

 as a winter food, and no effort should be spared to increase 

 the home consumption of herrings. They are probably the 

 cheapest form of animal food and have a very high nutritional 

 value. Many people will be surprised to learn that out of 

 12 million cwts. of herring landed, nearly 10 million cwts. 

 were exported annually before the war. The total catch is 

 far from being too much for the needs of our own country. 

 Taking three herrings to the pound, the total catch in the 

 United Kingdom before the war would only allow two herrings 

 a week to each adult individual of the population. 



The flat fish of our markets (with the exception of skates 

 and rays, which are a totally different kind of fish and are 

 nearly related to dogfishes and sharks) belong to the family 

 Pleuronectidae, the members of which undergo a remarkable 

 transformation in their early life-history, whereby the bi- 

 laterally sjmametrical larva, with the right and left sides of the 

 body similar and an eye on each, undergoes in its growth a 

 torsion of the head and some other parts, a flattening of the 

 body from side to side, and a great extension dorso-ventrally 

 so as to be converted into the familiar " fluke " form, with the 

 upper (usually the right) side of the flat body pigmented and 

 bearing both eyes, and the lower blind and more or less non- 

 pigmented or white. Our best-known marketable Pleuro- 

 nectids are : — 



1 By Dr. James Johnstone of the University of Liverpool (see for further 

 details Lancashire Sea-Fisheries Laboratory Report for 1917). 



