THE HERRING FAMILY. 419 



swarms round and round the tanks by day, but at uight they 

 separate, dart about rapidly in search of food and appear to 

 feed principally after dark. 



The young herrings appear to haunt the shore throughout 

 their first winter but on the approach of spring move away 

 to the open water, at least they are not caught in any numbers 

 near shore throughout the second summer. 



We may briefly summarise the life-history of the young 

 herring as follows, always remembering that the cycle is only 

 followed out in detail by the typical individual, and that a 

 margin must be allowed for variations such as have been seen 

 to occur in the later autumn-brood. 



The young larva, hatched at from 5 to 7 mm. in length, 

 lives near the bottom till about 10 mm. is attained by a rapid 

 increase in length. The attenuated post-larval herring then 

 migrates upwards through the mid-water to the surface, the 

 mid-water stage lasting from about 10 mm, to 23 24 mm., 

 and the surface-stage from 24 mm. to 27 28 mm., when a 

 movement shorewards takes place, and the littoral habit is 

 acquired. 



In dealing with the sand-eel, we summarised as follows : 



' The post-larval sand-eel remains at the bottom till a 

 length of about 10mm. is reached. Living alongside of it are 

 found great numbers of larval and post-larval herrings, usually 

 somewhat larger, and young Sagittw. There is a remarkable 

 superficial resemblance, caused solely by the attenuated form of 

 these three very diverse organisms, which is, of course, entirely 

 absent in the adult stages. 



'At a length of somewhat over 10 mm. the young sand-eel 

 commences its migration upwards through the mid-water, and 

 at this period its growth is very rapid. The average date 

 for this change of habit will be seen to be about the end of 

 April. By the third week in May. or sometimes earlier, the 

 surface will be reached, and in the three weeks' migration 

 through the mid-water the little fish will have grown from 

 10-11 mm. to 17-18 mm., a very rapid rate of growth. The 

 surface-period lasts from 17 mm. to about 30mm., and extends 

 from the third week in May till the second week in June 



272 



