866 
SCANDINAVIAN FISHES. 
the distance between the ventral tins and the tip of 
the snout. Accordingly too Osmerus , as a representa- 
tive of one of the earlier stages of the family, has 
greater averages in these respects than the Salmons. 
This is also the case with the length of the base of 
the anal tin'*. A general rule for the whole life of the 
Salmonoids is that the length of the maxillaries is re- 
duced with age in proportion to that of the body 6 , 
and the same rule applies to the length of the sub- 
operculum in proportion to that of the head or of the 
head reduced c , with a slight exception in the last case. 
The breadth of the interorbital space, on the contrary, 
increases with age in proportion to the length of the 
head or of the head reduced d . The length of the pe- 
duncle of the tail at the ventral margin e , and the least 
depth of the tail 7 , in proportion to the length of the 
head or of the head reduced, undergo alterations of 
growth which at the modification in the life of the 
Salmons — from fresh water to the sea — change di- 
rection: their averages increase as a rule in the earlier 
and earliest stages, but subsequently decrease, after 
attaining their maximum at the end of the life in 
fresh water. Here too Osmerus represents the earliest 
stages. 
Arithmetically expressed, this developmental rela- 
tion appears as follows: 
Average 
Distance between the dorsal fin and the tip of the snout in % of the length of the body : 
„ „ „ „ ,, „ „ ,, „ „ „ „ „ „ „ distance between the ventral fins and the tip of the snout. 
Base of the anal fin in % of the length of the body 
„ „ „ ,, „ „ „ ,, „ „ „ „ head reduced - __ 
Length of the maxillaries in % of the length of the body 
„ „ „ suboperculum „ „ „ „ „ •„ head — - 
,, ,, „ „ „ „ „ „ „ „ head reduced 
Breadth of the interorbital space in % of the length of the head 
„ „ „ „ „ „ „ „ „ „ „ „ head reduced 
Length of the peduncle of the tail at the ventral margin in % of the length of the body 
Least depth of the tail in % of the length of the head _ 
„ „ ,, „ ,, „ „ „ ,, „ „ „ head reduced 
Osmerus. 
Snlmo. 
47. s 
42.i 
96.5 
86.i 
11.7 
8.4 
79.2 
55.b 
9.3 
8.8 
28.5 
25.4 
41.9 
37.7 
25.i 
31.8 
37.7 
47.2 
8.4 
12.5 
23.2 
39.i 
34.8 
58.o 
Iu other points, again, it appears that the Smelts 
and the Salmons have each taken their own path 
of evolution, and that the Smelts in several respects 
— in some like the Charrs — occupy the higher rank 
in the scale of development. On continuing our search 
for the most different averages in the Smelts and Sal- 
mons, and on comparing the signification thereof with 
the alterations of growth to which the Salmons are 
subject, we find the following relations most deserving 
of notice: 
a Cf. Smitt, 1. c., p. 14. 
b „ ; v „ P- 10- 
c „ „ „ „ pp. 18 and 22. 
d „ ,, „ ,, PP- It and 20. 
1 ) , 1 , • , 1 1 p • 1 5 . 
f Cf. above, p. 833, the lower table, where these proportions may easily be calculated from the averages there given, and Smitt, 
Riksmus. Salmonider , pp. 19 and 23. 
