the Position of the Eyes in Pleuronectidee. 379 
is viewed from its right side. ‘The right eye is rather more 
round in outline—that is, a little shorter and broader than the 
left. This difference is caused by its being under pressure, 
wedged in as it is between the anterior frontal bones and the 
dorsal fin; and the pressure causes the interspinous part of the 
dorsal fin to form a small slightly upward-curved projection 
above the eye. 
The smallest of three young of Pleuronectes platessa, which 
I have also before me, has a length of only 10 millims., the 
measure being taken as above. ‘lhe ramifications of the mu- 
ciparous canal cannot be discovered on the left (blind) side of 
the head, whilst on the right side they are just traceable as ~ 
indistinct lines; but no ducts are to be distinguished. The 
whole head has a clumsy, toad-like shape, the parts of the 
mouth presenting soft swelling outlines. The right eye stands 
over the beginning of the lower third of the maxillary bone. 
The left eye stands at the top of the head, so much inclined to 
the right, that from the left side only a trifle more than one- 
third of the pupil can be seen; it stands in front of the dorsal 
fin, so that the front ray of the latter is just behind the end of 
the left and beginning of the middle thirds of the eye. 
On comparing with this the head of another young P. pla- 
tessa, which measures 14 millims. in length, one observes at 
_once that the head has a somewhat less clumsy appearance, and 
the ramifications of the muciparous canal are more clearly ob- 
servable. ‘The position of the left eye is so far changed that 
when the head is viewed straight from the left.side the pupil 
is invisible, only a part of the iris can be seen ;-and its position 
with regard to the dorsal fin is at the same time altered so that the 
latter touches the left margin of the eye, which cannot now be 
described as entirely situated in front of the dorsal fin ; for the 
foremost ray of the fin stands at the side of the eye, a little in 
adyance of the extreme posterior margin of the eye. When, 
therefore, the fish is examined from the blind side, the outline 
of the eye cannot be followed in its whole extent, the posterior 
extremity beg hidden from view behind the first ray of the 
dorsal fin. © 
In a third young P. platessa, measuring 40 millims. in 
length, the head presents almost the same pointed shape as in 
the adult fish. The ramifications of the muciparous canal are 
much more distinct, and the ducts are easily distinguished on 
the preopercular branch on both sides, as well as on the infra- 
orbital branch on the blind side. The right eye stands over 
the lower extremity of the upper jawbone; but, in spite of this 
_ more depressed position ofthe right eye, the distance between 
the eyes is nevertheless only a little greater than in the speci- 
27* 
