JOHS. 8CIIMIDT 107 



suited to the surroundings would be rejected, whereby the average 

 values for the different characters would of course be indirectly altered. 



The object which I had set befijre me was to elucidate as far as 

 possible, by means of suitable material, some of the conditions respon- 

 sible for the racial differences found among our marine fish species in 

 n'ature. From the outset, I had a clear appreciation of two jwints ; 

 first, that the investigation would have to be of an even more detailed 

 character than any of those previously carried out (though these might 

 seem detailed enough, for instance, in the case of the herring and plaice 

 investigations !). And secondly, that experimental aids would be neces- 

 sary, as without such, it would haixily be possible to arrive at any decisive 

 result. 



The necessity of experimental investigations again forced me to 

 abandon the two species in which the question of race has been best 

 investigated (statistically), viz. the herring and the plaice, since experi- 

 ments with these seemed out of the (.question at j)resent, at any rate with 

 the means at my disposal. In addition, I wished to have a species even 

 more " variable " and more local than the herring or the plaice. Both 

 of these are, as we know, pelagic for a more or less considerable part of 

 their life, and consequently subject to important passive or active dis- 

 locations which may lead to an intermingling of the individuals from 

 different populations. 



A species which appears to fulfil the required conditions is the com- 

 mon Viviparous Blenny (Zoarces viviparus, L.) with which I have now 

 been working since tlie autumn of 1914. I have made both statistical 

 and experimental investigations with this species ; only the former, 

 however, have up to the present been brought to a conclusion, and 

 only these are therefore so far advanced as to be suitable for jjubli- 

 cation. 



In course of time, a great number of specimens, over 25,000, have 

 been examined, with regard to several characters. A detailed account, 

 with the figures pertaining thereto, appears in Vol. xiii of the Comptes 

 rendus des travaux du Laboratoire de Carlsherg, Copenhagen, and I must 

 here restrict myself to mentioning some of the principal results. 



Zoarces viviparus is an extremely common fish in our Danish waters, 

 where it plays a far greater part than in the British. It lives as a rule 

 in quite shallow water, inside the 10 metre curve. Its distribution 

 in Europe has a marked north-easterhj character. It is found from the 



