62 



of 5.2 — 5.3 m.m. and that none of the animals reared artifi- 

 cially in aquaria sliowed a tracé of a yolk-sac af'ter having rea- 

 ched a length of 7.5 m.m. According to him , this leugth was 

 reached iu three or four days. Now I think it hardly possible 

 that in the open sea swimmiug larvae would grow more slowly 

 than such reared in aquaria ; therefore I incliue to admit that 

 the larva caught with. its yolk-sac was a couple of days old at 

 the most. 



Numerous larvae of the next-following stage were taken to 

 the West of Schokland , and between Kampen and ürk. They 

 have a length of about 16 mm.; their age will be about 20 days 

 or a month, when the time necessary for the development of the 

 egg is reckoned also. I figured this stage in Fig. 4. The dorsal 

 fin is formed, and may be distinguished even with the naked eye ; 

 the pectoral fins have the shape of fleshy plates, and the ventral 

 fins are still wantiug. The tail begins to curve upwards and 

 shows at its underside the first two cartilaginous pieces. 



The ventral fins are clearly visible as soon as the young her- 

 ring has got a length of 24 m.m. In larvae only 20 m.m. long 

 it is possible, at least with some trouble, to ascertain the place 

 where these fins will be found in a later period. When the lar- 

 vae become larger than 24 m.m. their development advances very 

 regularly. The largest herrings which still must be considered as 

 herring-larvae have a length of 35 — 36 m.m. The figures 5 & 6 

 of PI. V are drawn after such a fish, taken with numerous others 

 oatside the Ketel : they are in this condition well worth studying 

 a little more earefully , as they shed light over a very interes- 

 ting circumstauce in the life-history of our herring. 



I call the development of the herring a metamorphosis and 

 the young fish a larva , as new organs are formed during this 

 period and others assume in it a quite different form. The change 

 from larva in young fish with the Zuiderzee-herrings takes place 

 when their length is about 35 a 36 m.m. I call it a larva, as 

 long as it is still naked, i. e., bears no scales , as long as it 

 possesses embryonic pectoral fins and its form is comparatively 



