422 
SCANDINAVIAN FISHES. 
of the body which is characteristic of the American form, and which, 
in spite of the variations that accompany the usual changes of growth 
and the difference of sex, cannot be regarded as entirely wanting in 
significance. As a rule, in Drepanopsetta platessoides , the greatest 
depth of the body is more, in Drep. limandoides less, than 35 / of 
the length of the body; and in consequence, the length of the head 
in the former is less than 63 %, in the latter more than 64 % ", the 
postorbital length of the head in the former less, in the latter more, 
than 37 ' %, and the length of the branch of the lower jaw on the 
eye side in the former less than 28 %, in the latter more than 30 % 
— all in proportion to the greatest depth of the body. The same 
relation is also expressed by the fact that the least depth of the body 
{across the peduncle of the tail) in Drep. platessoides is more than 
75 %, in Drep. limandoides less than 72 of the length of the 
branch of the lower jaw on the eye side. Another character which 
also seems to be constant in adult specimens, lies in the fact that 
the greatest thickness of the body in Drep. platessoides is more, in 
Drep. limandoides less, than 2 3 of the length of this branch of the 
lower jaw. We have here to consider the same question as we have 
just discussed with reference to the distinction between Pleuronectes 
glad aits and PI. eicatricosus. It may indeed be true that during 
youth these forms cannot be distinguished — in any case we have not 
sufficient knowledge of their early stages to decide. But during the 
latter part of their development they are distinctly separated, and, 
strange to say, the difference between Drep. platessoides and Drep. 
limandoides runs parallel to that between Pleur. glacialis and Plenr. 
eicatricosus , just as the latter difference has proved above to be parallel 
to that between Pleur. platessa and Pleur. flesus. In all three cases 
the differentiation of form has taken the same course. In the Plaice 
and the Flounder it has indeed advanced further, but not even these 
species have escaped the suspicion of being “links in a common series 
of forms, made up of the finest shades of difference.” 
The following table shows partly the most important changes 
of growth in Drepanopsetta limandoides as it increases in length from 
228 to 315 mm., and partly the. relation of this form (on an average) 
to Drep. platessoides while between 310 and 396 mm. in length: 
A v crag e 
Measurements 
of a d speci- 
men of Drep. 
platessoides 
from Halifax. 
Drep a nop sett r 
limandoides. 
3 specimens 
^ (c? +99) 
of Drep. pla- 
tessoides. 
Ohs 
• 
3 specimens 
(99?). 
3 specimens 
(999)- 
Length of t lie body, expressed in millimetres 
242.2 
294 
341.7 
319 
Total length of the head in % of the length of the bodv 
21.7 
22.o 
21.1 
22,o 
Ijuv. 
l 9 
< 
sen. 
d 
Postorbital length of the head ,, .. ,, „ „ „ „ 
12.9 
13.3 
12.7 
13.i 
ijuv. 
1 9 
< 
sen. 
C? 
Greatest depth of the body. „ „ ,, „ „ ,, ,, ., 
32.i 
31.6 
37.o 
35.4 
9 
> 
d 
Least. ,, „ „ ,, ,, „ „ „ „ 
T.i 
7.3 
8.o 
7.5 
9 
> 
d 
Length of the branch of the lower jaw on the blind side ,. „ ,, 
11.8 
12.7 
11.6 
11.9 
/juv. 
\ 9 
< 
<- 
sen. 
d 
„ eye „ „ „ „ „ 
10.3 
10.9 
9.9 
9.9 
juv. 
< 
sen. 
Distance between the dorsal fin and the tip of the snout _ ,, „ „ ,, „ ,, ,, ,. 
6.9 
C>.o 
5.7 
6.o 
9 
< 
d 
Length (base) of the dorsal tin __ 
70.5 
73.i 
72.9 
9 
■> 
d 
Height (longest rav) of the dorsal fin ,, „ „ „ „ „ „ „ 
9.1 
9.0 
9.4 
10.9 
juv. 
> 
sen. 
Distance between the anal tin and the tip of the snout „ „ „ ,. ,, „ „ 
29.o 
27.8 
29.0 
27.2 
Ijuv. 
1 9 
A A 
sen. 
d 
Length (base) of the anal tin ,, ,, 
52. s 
53.o 
57.3 
50.7 
9 
> 
d 
Height (longest ray) of the anal iin „ ,, ,, „ „ „ ,, „ 
9.3 
9.4 
9.2 
10.9 
juv. 
sen. 
Length of the pectoral fin on the cvc side „ „ „ „ „ „ ,, 
10.8 
9.i 
10.7 
12.2 
juv. 
> 
sen. 
blind 
8,1 
8.o 
9.7 
juv. 
Ijuv. 
\ 9 
> 
sen. 
„ ,, „ ventral ,. „ ,, eye ,, „ „ „ „ „ „ „ „ 
7.3 
7.vS 
7.s 1 
8.8 
A A 
sen. 
d 
blind 
8.0 
8.4 
8.5* 
9.4 
/juv. 
1 9 
Ijuv. 
1 9 
< 
sen. 
d 
sen. 
d 
„ „ „ caudal at the middle „ „ ,, „ „ „ ,, „ 
15.2 
16.8 
15.i 
15.7 
<* 
Total length of the head in % of the greatest, depth of the bodv 
(>7.g 
69.9 
57.i 
62.2 
Ijuv. 
\ 9 
< 
sen. 
d 
Postorbital length of the head „ „ „ ,, ,, „ „ „ ,, 
40.2 
42.2 
34.6 
37.i 
Ijuv. 
1 9 
< 
< 
sen. 
d 
Least depth of the body in % of the length of the branch of the lower jaw on the eye side 
69.7 
(>(>.7 
80.6 
76.2 
Ijuv. 
1 9 
> 
sen. 
d 
Greatest thickness of the bodv .. ,. ,, „ ,, „ „ 
61.7 
59.n 
70.i 
69.8 
Ijuv. 
1 9 
> 
sen. 
d 
The table shows distinctly that in hardly a single one of the i 
average relations does Drepanopsetta platessoides fit exactly into the 
series of the changes of growth. In some cases the series is broken 
by the average measurement of this form, which in these respects 
represents the characters both of the young specimens and the fe- 
males; while in others the series does indeed run in the same di- 
rection, rising or falling in all three of the first columns, but is ir- 
regular, with too wide or too narrow a gap between the second and 
third columns, this being due to the fact that the characters of a 
male specimen have been included in the third column of averages, 
The minimum proportion in this respect in all the specimens examined by Collett was 65 %. 
In its capacity of a change of growth this relation is less than would have been the resrdt of a uniform course of development. 
