of the Fishery Board for Scotland. 



53 



tongue are smaller than those of the herring, but the sprat has no 

 vomerine teeth (Giinther, Cat. of Fishes in Brit. Mus., &c.). 



Dr Heincke * gives a method for determining the specific value of the 

 external characters, and for showing how far the variations, which he found to 

 occur largely in both sprats and herrings, are common to both. Since writing 

 the above description I have subjected a large number of my measure- 

 ments to the same test, and I find the result in many respects disagrees 

 to a considerable extent with those of Dr Heincke. For instance, Heincke 

 finds by his method of comparison (taking the variations in the characters 

 of the fish as sections of a straight line) that, in the case of the keeled 

 scales between the pelvic fin and the anal aperture, there is a tract 

 amounting to fths peculiar to the sprat alone, and a tract equal to |ths 

 peculiar to the herring, whilst there is a tract amounting to ^th common 

 to both ('common ground of variation'). This is deduced from his hav- 

 ing found the keeled scales to vary in number in the sprat from 9 to 12, 

 and in the herring from 12 to 16. Now, I never found examples among 

 the sprats which I examined of so few as 9 or even 10 keeled scales, and 

 the maximum number was 13 ; nor did I ever find fewer than 13 nor more 

 than 15 in the herring. Following, then, Dr Heincke's method, the pro- 

 portions I get are fths peculiar to the sprat, fths peculiar to the herring, 

 and |th common to both. Dr Heincke ascertained that 7 per cent, of his 

 specimens fell within the common ground of variation. In my case, how- 

 ever, only 1 sprat and 1 herring out of 150 of each had 13 of these scales, 

 so that the percentage I get, as included in the common ground, is only 

 •66. I get, therefore, a much smaller result, both in the amount of com- 

 mon ground and in the percentage of individuals included in it, and con- 

 sequently the number of keeled scales appears from my figures to be of 

 much more specific value than they are considered to be by Dr Heincke. 



But this difference between his results and mine is more marked when 

 we come to examine the pelvic (ventral) fin rays. Dr Heincke gives the 

 number of rays (deduced from his examination of, I understand, 125 

 herring and 13 sprats) as 7 to 10 in the herring and as 6 to 7 in the 

 sprat. Among over 700 sprats I did not find more or fewer than 7 rays, 

 and in 150 young and 100 adult herrings never any other number than 

 9. I have, therefore, considered the number of rays in this fin as being 

 of absolute specific value, and I would feel justified in considering the 

 occurrence, if I had found it, of, say 1 herring with 7 rays as an abnor- 

 mality, and not as vitiating my conclusions as to the absolute specific 

 distinctness of the sprat and herring in this particular respect. In fact, 

 the question of the specific value of a character depends altogether on the 

 number of cases of its common occurrence in different species. Dr 

 Heincke finds the rays in the pelvic fin to vary, — I do not, even after 

 examination of a much larger number of specimens, and, therefore, I 

 think his cases must be considered as very exceptional. 



I still further disagree with Dr Heincke when he says that no specific 

 value can be attached to the number of vertebras. He has found varia- 

 tions in the number of vertebras which I have not, but still I think 

 that, even taking his figures, the smaller number, even of his maximum, 

 in the sprat, as compared with the minimum number in the herring, 

 justifies us in placing considerable weight on this character as one of 

 specific value. 



In some other points my results differ from those of Dr Heincke, but 

 these principally apply to those characters which from their more common 

 occurrence in both species, I agree with him are not of great specific im- 

 portance. The following, however, are worth noting. 



* ' Die Varietaten des Herings,' Jahres. d. Com. in Kiel, 1874-76. 



