SCANDINAVIAN FISHES. 
3 6 6 
described. The former assumed that the eye in its 
wanderings penetrates a part of the still membran- 
ous frontal bones of the blind side, while the latter 
in his figures shows the passage of the eye just 
under the lower ends of the interspinal bones of 
the dorsal fin. 
These radical alterations are accompanied by a con- 
siderable difference in the shape of the body within the 
various genera of this series; but the intermediate forms 
prevent us from sharply limiting the groups we should 
like to define, and most writers agree in referring all 
these forms to one common family. 
Fam. P L E U R 0 N E C T 1 1) M. 
Body in adult specimens deep and strongly compressed , with the eye side , in the natural position , turned upwards 
and the blind side doivnwards. Dorsal and anal fins long , occupying at least the greater part of the length of 
the fish. Branch iostegal rays (> — 8. Pseudobran chics present or wanting. Air-bladder generally wanting. Pyloric 
appendages few or wanting. 
This family, which was established by Cuvier 
under the name of Poissons plats , RondeletV Pisces 
plant , spinosi , bore the name of lygrrondsTs in as early 
a writer as Aristotle; but its present systematic name, 
Pleuronectidce , is no older than in Bonaparte’s 1 ' time. 
The shape of the body is no deeper here than in 
many other fishes, in certain Cluetodonts and Carangidce 
for example; and in the Rays flatness of body is conjoined 
with the same habits and in great part the same co- 
loration and manner of locomotion as those of the Flat- 
fishes. The asymmetry of the latter, however, as we 
have remarked above, is always enough to distinguish 
them. Whether this characteristic is immediately con- 
nected, as some have assumed, with the general ab- 
sence of the air-bladder in the Flatfishes, is a very 
doubtful point, for both in Paralichthys ( Pseudorhom- 
bus ) dentatus (melanog aster) and in Bothns ( Rhombus ) 
maculatus Agassiz'' found the air-bladder “well-deve- 
loped” in the fry even before the eye had begun its 
wanderings. Again, the air-bladder is not wanting in 
all the rest of the members of this family. Costa e 
found it present in several Mediterranean species, even 
when full-grown, its size being greatest in Bhomboid- 
ichthys podas; it is hardly a functional organ, however, 
and during the course of development it shrinks or 
changes into a glandular organ, according to Costa, a 
lymphatic ganglion. The loss of the air-bladder, like 
the asymmetry, is thus a change of development. This 
is also true of the different colours of the two sides of 
the body. So long as the fry are symmetrical, the 
pigment is equally distributed on each side of the body; 
and even during the wanderings of the eye, the dif- 
ference is slight. During this period dark transverse 
bands usually appear on the dorsal and anal fins and 
the neighbouring parts of the sides, as far inwards as 
to the end of the interspinal bones; and these trans- 
verse bands belong to the blind as well as to the eye 
side. During the advancing metamorphosis to asym- 
metry, however, the blind side loses more and more of 
its pigment, until at last, in most cases, it is bleached 
quite white, and the colour of the body collects on the eye 
side. In recent times, chiefly through the researches of the 
Frenchman Pouciiet', science has been enabled positively 
to refer these changes of colour to the nervous system. 
The lively description Heincke has given us of 
the changes of colour in Gobius flavescens (see above, 
p. 252) is a striking example of the power possessed 
by fishes in general of adapting their own colour to 
that of their surroundings; but the Flatfishes enjoy this 
faculty to a still higher degree, especially during youth. 
0 Regn. Anim., edit. I (1817), p. 218. 
b De Piscibus (1554), p. 809. The Rays were pisces plant , cartilaginei. 
c Sagg ., 1831; Syst. Icht. Isis 1833. Raeinesque called the family Pleuronectia (1815), and Risso used the French name Pleuro- 
nectides (182(3). 
d Devel. Flound., 1. c., p. 11, pi. VI and VII. 
e Fa. Regn. Nap ., Malacott., Sottobr., Pleuron., p. 64. 
f On the connection of nerves and chromoblasts, Monthl. Micr. Journ., Dec. 1871, p. 285; Des changements de coloration sous V in- 
fluence des nerfs , Journ. de 1’Anat., Phys. 1876, pp. 1 and 113, pi. I — IV. Cf. Smitt: Ur de hogre djurens utvecldingshistoria , p. 271. 
