75 



ia the list given above. Their forinulae are: 3 b III B, 2 b IB, 

 2 c UIA, 3 c IC, 3 b III C and 2 c IV C, each of thera appro- 

 achiiit; very nearly to formulae of the said list. Looking at the 

 formulae of these 85 little fishes a bit more carefully , one is 

 struck by the fact that their rautual agreement is greater still than 

 is the case with the full-growu herrings. This may partly be 

 due to the circnmstance, that in later life small difïerences might 

 develop between individuals which in youth reseuible one another 

 more perfectly. It is also possible that herrings originally stran- 

 gers in the Zuiderzee, might in the Northsea mix among shoals 

 about to return to the Zuiderzee , the sea in which they were 

 born. Having often found sprats among the shoals of Zuiderzee- 

 herrings , and knowing that these uo doubt mixed tbemselves in 

 the Northsea with the herring-shoals bound for the Zuiderzee, no 

 objection can be raised , I think , against admitting that Northsea- 

 herrings also may have joined the througs which approach our . 

 coasts and enter our gates. 



But to return to the small ones. In general they agree quite 

 well with the full-grown ones; but comparing the formulae of 

 p. 69 carefully with those of p. 74 , a slight difference in the 

 index for the anus as well as in that for the length of the anal 

 fin is discovered : the anal aperture in the full-grown fishes of 

 the Zuiderzee has in 2^,^% of the cases I studied the index O ; 

 in 48'Vo the index I; in 45<'/o the index II, and in 4V.2% of the 

 cases the index III. In the small herrings this index, however, 

 was never found to be O; in 3"/„ of the fishes I have investigated it 

 was I; in 48^'o the index was II; in 46''/o it was III, and in 3°/o 

 it was even IV ; sunimarizing these resalts, my conclusion would be , 

 that whereas the index for the anus for the small herrings of the 

 Zuiderzee is II & III, for the full-grown herrings it is I & II ; and , 

 as my conviction that these young and full-grown herrings be- 

 long together is uot in the least weakened by this divergence, I 

 only can explainit by admitting that the Zuiderzee-herring during 

 its grovvth moves its anus slightly backwards. The anal fin in 

 the young herrings in 01 cases out of 100 has as its index B, and 



