61 



As also is reconlod ia the table of p. 59, the temperature of 

 the water at the phices where herriug-hxrvae were observed varied 

 between 23 May and 18 July from 14°5 to 18°5 C. VVhen 

 herriug-spawn was eolleeted (ou 1, 15 and 24 May) the tempera- 

 ture of the water was resp. 12°, 12°5 and 14°8 — rather high 

 temperatures compared with those (9°4 C.) whieh Hoöniaun ob- 

 served wheu hatchiug herriug-óva. A higlier temperature is very 

 favourable, as well for a more rapid developmeut of the eggs, as 

 for the growth of the hatched larvae. Meyer tells us that the 

 egg of the herring requires for hatching forty days when the 

 temperature is 3°5 C, fifteeu days when the temperature is 7 — 8°, 

 and eleveu days when it is 10—11°. HofiFmann observed, that 

 12 days were necessary when the temperature was 9°4 C. 

 This is quite in accordance with Meyer's observation. The latter 

 moreover ascertained, that for the development of the egg of the 

 herring only 6 — 8 days are required when the temperature slightly 

 exceeds 11°: most probably the eggs of the Zuiderzee-herrings 

 in the course of May '88 will have developed at that rate. 



No doubt the Zuiderzee-herring spawns during several weeks, 

 and this might also be coucluded from the dimensions of the 

 larvae eolleeted. On 23 May larvae were caught measuring 18 — 21 

 m.m. and at the end of June still such were met with, which had 

 exactly the same length. The smallest larva I eould identify as 

 herring-larva was taken May 24 and had a length of 7.25 m.m. 

 I have figured it (PI. IV. fig. 3) and, as that figure shows, the little 

 animal was still furnished with a yolk-sac of considerable size 

 — more than one m.m. long. Most probably this larva had hatched 

 already a few days before , as Hofi'mann says , that the larvae 

 which he reared, on comiucr out of the egg, had a length 

 of 6.2 to 6.4 m.m. only. The well-filled and even with the 

 naked eye visible yolk-sac proves, however, that its age cannot 

 vet have been considerable. Kupöer ^) says, that the herring- 

 larvae born in the brackish water of the Schlei have a length 



1) Kupffer, C, Ueber Laichen und Entwicklung des Herings iu der westlichen Ostsee. 

 Jahresber. d. Comm. IV— VI. 1878. S. 33. 



