THE HERRING FAMILY 157 



For if this theory were true, it is clear that the herrings could 

 not be in the ripe and spawning condition at every stage of their 

 journey, and they actually arc full and ripe at each place where 

 the summer fishing is carried on at Wick in July, at Lowestoft 

 in November. The fish that spawn at Lowestoft in November 

 cannot be the same fish which spawned off Dunbar in September. 

 We must conclude that the fish which escape the nets of the 

 fishermen after spawning in any district depart and go back by 

 the way they came. But still they must even on this more 

 correct view come and go, and we have to consider whence 

 they come and whither they go. We have good reason to 

 believe that adult herrings do not remain in the North Sea in 

 very large numbers except in the spawning season, at least not in 

 the narrower southern parts of the North Sea. We are com- 

 pelled therefore to conclude that they retire to the deeper, more 

 northern waters of the Norwegian Sea. The migration in fact 

 appears to be towards the coasts and away from the coasts. 

 Different shoals seek different spawning beds at different times 

 of the year. But to what distance their migrations extend, and 

 whether they remain in shoals after they leave the spawning 

 grounds, or disperse, are questions which we cannot answer. 



The appearance of the egg of the herring under the micro- 

 scope is shown in Fig. 84. The yolk is composed of a large 

 number of small spherules, as in the case of other adhesive eggs, 

 but there are no separate oil-globules. The space between the 

 egg-membrane and its contents is greater than it usually is in 

 buoyant eggs. The egg when shed is globular, but its surface 

 becomes flattened where it is attached to other eggs or to solid 

 objects. The size of the egg varies somewhat in different 

 localities; at Ballantrae it was found to be 1-5 mm. (yfo- inch) 

 across after fertilisation. In the developing egg the embryo is 

 long compared to the size of the yolk, so that before the tail has 

 grown out into a free projection the head and tail almost meet 

 round the yolk. 



The time occupied in development before hatching varies 

 with the warmth or coldness of the water. Eggs obtained in 

 August off the Farn Islands and kept at 52 to 58 hatched out on 

 the eighth and ninth days. Eggs obtained at Plymouth on 

 January 26th hatched in from twelve to fourteen days at the 

 temperature of about 48?. In experiments made at Kiel it was 



