76 



in 37 cases C; in tlie full-growu fishes in 12 cases out of 100 

 it is A, in 75 cases B, and in only 13 cases C. So its index in the 

 full-grown fishes seenis to be slightly larger — the fin therefore 

 relatively shorter : I should not like , however , to express myself 

 here with the same decision , as in the case of the position of the 

 anal aperture , because it is extremely difBcult to measure the 

 length of a fin in fishes as small as the young herrings which I 

 investigated — a slight difference in the measurement taken might 

 cause a difference of consequence in the figures I have given. 



Be this as it may — as a general conclusion of my researches 



on the Zuiderzee-herriug I believe I can legitimately state that: 



1°. The Zuiderzee-herring is a spring-herring , spawning in 



brackish water. 

 2°. The greatest dimensions the Zuiderzee-herring-larva acquires , 

 before assuming the appearance of a young herring, are much 

 smaller than those of the full-grown Northsea-herrinjy-larvae. 

 3°. The young herrings born in the Zuiderzee stay in that sea 

 uutil their length is from 100 to 120 m.m., then to exchange 

 it for the Northsea. 

 4°. Part of these herrings return to the Zuiderzee as so-called 

 sprats , having a size of about 150 a 160 m.m.; most ot 

 them only return, when full-grown and approaching matu- 

 rity. They begin to enter the gates toward the end of 

 September , and continue doing so till in April , only stop- 

 ping this incursion when the water of the Zuiderzee gets 

 too cold. The later they enter the more they approach ma- 

 turity. 

 5°. Youuger and older sprats enter with the herrings, and pro- 

 bably such herrings as are not born in the Zuiderzee occa- 

 sionally do so also. 



Sprat. Only rarely I discovered little fish of this species among 

 the immature fishes caught with the kuilnets. In the following 

 list the formula I calculated for each is communicated. 



