ra : Bap a 
distance in advance of its primitive position. 
4 > other, the dorsal fin gradually exten 
_ Nor edge of the orbit of this eye. This young 
3 Presented a stage in which the eye from 
THE 
AMERICAN NATURALIST. 
Vou. x — DECEMBER, 1876. — NO. 12. 
THE DEVELOPMENT OF FLOUNDERS. 
BY ALEXANDER AGASSIZ. 
a manner in which the eyes of a flounder become placed on 
one side of the body has formed a fertile subject for theories. 
Ido not at present propose to discuss the explanations given to 
account for the facts, but merely to state the results of observa- 
ons made while studying the development of a number of spe- 
ead of flounders common to our coasts. In the case of five spe- 
cies the passage of the eye from one side to the other is not, as 
wged by Malm, a simple tendency of the eye of the “ blind side” 
(the side upon which the flounder lies) to turn towards the light 
and thus carry the surrounding parts of the head with it. The 
eye placed on the blind side actually travels from its original 
place (symmetrical with the eye of the opposite side) frontwards 
and upwards on the blind side, resorbing the tissues in its way, 
sodad tissues forming behind ; there follows this movement of trans- 
lation a certain amount of torsion of the whole of the frontal part 
of the head, which commences only after the eye of the blind 
side has nearly reached the upper edge of that side, quite a 
: This torsion of 
course takes place most readily, occurring as it does during a 
ill cartilagi- 
stage when the whole bony fabric of the skull is sti 
nous, and it is the torsion which ends in bringing the eye to the 
°Pposite side. In four of these species of flounders the dorsal 
fin did not at that young stage extend to the posterior edge of the 
orbit of the eye coming from the blind side. 
had thus by the same process 
ht from the one side to 
ded beyond the ante- 
flounder thus soon 
the blind side appeared 
another species, after the eye 
L translation and of torsion been broug 
Copyright, A. S. PACKARD, Jn. 1876. 
