SALMONS. 
835 
scales, expressed in their number. The scales are gene- 
rally larger in Salmo salar than in St trutta, but larger 
even in the latter than in S. umbla. In a longitudinal 
row extending along Vio °f the length of the body, we 
find 1) on the anterior part of the belly above the la- 
teral line in S. salar on an average 18 scales, in S. 
trutta 18 — 21, and in S. umbla 30, 2) on the tail in 
S. salar 15 or 16, in S. trutta 16 or 17, in S- umbla 
26. Thus the Charrs have probably been developed 
from a race nearer to the Gralax than to the Blanklax ; 
but the development has followed the same course and 
produced the same results in the differentiation of form. 
The natural relation between the Charrs is indeed 
more complex, but all the more instructive. In Scan- 
dinavia we have two forms, the Northern Charr ( Salmo 
alpinus ) and the Saddling ( S . salvelinus), whose right to 
a specific rank is almost as certain as the difference 
between the Gralax and the Blanklax , and which occupy 
the same developmental relation to each other, 8. alpi- 
nus representing the younger stages of growth, S. sal- 
velinus the older ones. Besides these forms however 
— in order to gain a correct understanding of the re- 
lation between them — we must take into consideration 
a third form which strictly belongs to Greenland and 
the northern regions of North America, and for which 
we may employ the specific name given it by Fabri- 
cius rt , Salmo stagnalis 1 '. 
On closer examination of these three Charr forms, 
we see that in many respects 0 the averages run in an 
uninterrupted series from alpinus through stagnalis to 
salvelinus, i. e. alpinus represents the youngest stages, 
salvelinus the oldest. Here, for the sake of brevity, 
we can only give one example. 
The least depth of the tail in proportion to the 
length of the head diminishes as a rule in the Charrs 
with increasing age. In order more carefully to test 
the particulars of this relation and others, I have di- 
vided the material possessed by the Royal Museum 
into six groups according to age. As we have no cor- 
responding terms in popular phraseology, I have denoted 
these groups by Roman numbers. The first group (I) 
contains the specimens under 228 mm. in length. 
Among all these specimens (of all forms and interme- 
diate forms) the average length of the body is 188 mm. 
The second group (II) contains the Charr between 228 
and about 355 mm. long. The average length of body 
in this group is 303 mm. In the third group (III) 
the maximum length of body is about 458 mm. and 
the average length 387 mm. In the fourth group (IV) 
these measurements are respectively about 538 mm. 
and 494 mm. The fifth group (V) contains only three 
specimens, all about 650 mm. long. The sixth group 
(VI) consists of only one specimen, a male from Spitz- 
bergen, measuring 757 mm. 
The alterations caused by growth in the relation 
between the least depth of the tail and the length ot 
the head, are most regular in our specimens of stag- 
nalis, being in this form: 
Average in 
ii. 
III. 
IV. 
V. 
C? 
34.0 
32.9 
30.4 
9 
35.9 
33.6 
— 
32.6 
The averages in the 
second group (II) 
are: 
Average 
n 
alpinus. 
stagnalis. 
salvelinus. 
d"-~ 
36.5 
34.o 
29.4 
9 - 
37.4 
35.9 
29.9 
The form 
series, expressed in 
averages 
for all oui 
specimens, is as follows: 
Average 
alpinus. 
stagnalis. 
salvelinus. 
Least depth of 
of the head. 
the tail in % of the length 
36.7 
33.2 
29.2 
AH these averages follow a regular course, con- 
stantly decreasing. Such is the case where the form 
series has retained its original type, and in the rela- 
tions where the males evidently represent the highest 
stage of development. In several relations, however, 
the females have a special representative in stagnalis, 
arid the original form series has thus been modified 
in a singular manner. We have an example of this 
in the proportion between the length of the maxillaries 
“ Fauna Groenlandica , p. 175. 
b In order to simplify the question, we here omit some intermediate forms, the significance of which we may disregard for the 
time being. 
c In the work quoted above ( RiJcsmus . Salmon.) I have adduced 18 such points. 
