[21] SCIENTIFIC EXAMINATION OF THE GERMAN SEAS. 545 



brackish bays. The eggs of the herriDg can stand a great difference of 

 degree of saltness. 



In the North Sea they develop in water whose percentage of saltness 

 is 3.5, on the eastern coast of Eiigen in water containing 0.8 per cent, 

 of salt, and on the coasts of Prussia and Scotland in water having an 

 even smaller percentage of saltness. 



In the northern part of the North Sea the herrings which spawn in 

 autumn reach maturity much sooner than in the southern part. Ou the 

 east coast of Scotland they spawn as early as July and August, on the 

 east coast of England in September and October, and in the neighbor- 

 hood of the Channel even late in autumn. 



The autumn eggs are generally deposited in warmer water than the 

 spring eggs ; but whilst the young spring herrings grow up with in- 

 creasing warmth of the water, the autumn herrings develop in water 

 whose warmth is decreasing. 



The herring eggs can stand a great difference of temperature. Their 

 development is not interrupted when they are cooled off by a tempera- 

 ture approaching zero, nor by a temperature rising as high as 15° 0. 

 In cold water their development is slower than in warm water. With 

 a temperature of 3°.5 the young Baltic herring leaves the egg after 

 forty days, at 7° to 8° in fifteen days, 10° to 11° in eleven days, and with 

 a still higher temperature in six to eight days. 



The development of eggs which have been laid in November or De- 

 cember, therefore, generally takes somewhat longer than the develop- 

 ment of eggs laid in spring. This explains the circumstance why the 

 larvae which have come from November or December eggs do not have 

 the same length in April as the larvae which have come from the Octo- 

 ber spawn. 



Autumn larva? from the Bay of Eckernfordc (Eig. XIV, lower figure) 

 differ from spring larva? from the Schlei (Eig. XIV, upper figure) in the 

 following particulars : In the autumn larva? the ventral fins do not be- 

 gin to appear until they have reached a length of 33 to 31 millimeters, 

 whilst in spring larvae they appear when the little fish are only 25 to 26 

 millimeters long. 



The autumn larvae have comparatively smaller heads than the spring 

 larva? ; they do not leave the larva stage until they have reached a 

 length of at least 44 millimeters, and even when they measure GO milli- 

 meters they are frequently not yet fully covered with scales. 



5. — Comparison of the herring and the sprat. 



The sprat resembles a herring of the same length to such a degree 

 that a person who is not thoroughly acquainted with the differences be- 

 tween the two kinds of fish cannot easily distinguish the one from the 

 other. 



In carefully comparing the two we shall find the following differences 

 (Fig. Ill and Fig. XIII) : 

 S. Miss. 59 35 



