WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES. 3 
which were made into separate aquaria by tying netting over the ends 
and were supported by a floating frame. After they had remained here 
for a time they were removed to the laboratory and kept under 
observation in running water. 
The period at which the eye turns is one of great mortality among the 
young fish captured, so that most of those in this stage died before re- 
moval from the net. Since there is as yet no bony orbit, the eyes are 
absolutely unprotected. As the eye which is to change its relative 
position must for a time be on the dorsal side of the head, held in 
position merely by the skin and a limited amount of connective tissue, 
it is not strange that in a number of instances young fish were taken 
alive which had lost the migrating eye some time before their 
capture. 
The actual turning is a comparatively rapid process in the species I 
have observed, though, as will be seen later, a long preparation is made 
for it. For instance, those fishes taken in which the migrating eye had 
reached the sagittal plane of the head swam in an upright position, 
though they came to rest more often on the future eyeless side. 
Within three days after the capture of a fish in this stage both the 
orientation in swimming and the position of the eyes became essen- 
tially that of the adult. 
The growth of the fish after turning is rapid. A sand-dab measuring 
10 mm. in length and 5 mm. in depth (7. e., the measurement taken along 
the dorso-ventral axis) was confined in a lamp-chimney aquarium for 11 
days and then was found to measure 22 mm. in length and 12 mm. 
in depth. If the third dimension, the breadth or thickness of the 
fish, be assumed to increase in the same proportion, which is a reason- 
able assumption, the volume of this individual increased more than ten- 
fold during the 11 days. The winter flounder of corresponding stages, 
according to my observations, does not grow quite so rapidly. It 
reaches a length of about 75 mm. by the end of August, when it 
is at most 7 months old. 
There are six species of flatfishes comparatively common at Wood’s 
Hole, according to Smith (’98). Three of these, Pseudopleuronectes 
americanus, Limanda ferruginea, and Achirus fasciatus, are dextral (7. e., 
the fish lies normally with the right side uppermost), and three, Paral- 
ichthys dentatus, Paralichthys oblongus, and Bothus maculatus are 
sinistral. 
Of these six species, Paralichthys dentatus probably breeds in the open 
sea, as small fish are not found. Paralichthys oblongus and Bothus 
