472 



TELEOSTEI 



even the free-swimming larva are structurally symmetrical ; but in later 

 stages the eye of one side is brought round until it occupies a position 

 above the eye of the other side. Thus in the adult the two eyes lie 

 on the same side, which is now carried upwards, and the lower side 



A. 



B. 



rna 

 ^ rnac. 



rna, 



Iff. 



FIG. 501. 



Pleuronectes platessa, L. (After F. J. Cole and J. Johnstone.) A, dorsal, and B, ventral view 

 of skull, showing the torsion of the front region, ar, large process of right side ; as, alispheroid ; 

 bo, basioccipital ; co, exoccipital ; ep, epiotic ; et, ethmoid cartilage ; f.c, carotid foramen ; f.g, 

 glossopharyngeal foramen ; f.j, jugul.,r foramen ; f.t.f, trigeminal and facial foramen ; f.v, vagal 

 foramen ; h, socket for hyomandibular ; l.f, left frontal ; Lie, left lachrymal ; l.pf, left prefrontal ; 

 me, mesethmoid ; op, opisthotic ; pa, parietal ; pro, prootic ; ps, parasphenoid ; pto, pterotic ; 

 */ "ght frontal ; r.lc, right lachrymal ; r.na, right nasal ; r.na.c, right nasal cavity ; r.pf, right 

 prefrontal. 



is left 'blind.' The migrating eye may remain near the dorsal edge 

 of the head, as in the more primitive genus Psettodes (Fig. 502) ; or 

 it may move farther down on the 'ocular' side (Pleuronectes, Solea, 

 Fig. 503). In this case the eye of that side also moves down, so as to 

 allow more room; and sometimes, as in Synaptura (Fig. 504), the two 

 eyes may come very close together, and the orbits become confluent near 



