328 



THE EYE IN EVOLUTION 



Fig. 389. — The Stalked-eyed Teleost, Sj i-lopjjthaimus pahadoxvs, the 

 Larva of Ib/acaxthus. 



Showing the eyes at the termination of the two stalks (after Brauer). 



Figs. 3'JO to 392. — Diagram of the Development of the Teleost, 

 Idiacanthus fjsciola (after Beebe). 



Fig. 39U. — Young stalk-eyed larva, Sli/lopIitJialmns paradoxus, 16 mm. long. 



Fig. 391. — Larva with degenerating eye, 40 mm. long. 

 Fig. 392. — Adult male Idiacanthus. 



Plaice 



Sole 



rooted on the skull (Figs. 389, 390). In the adult the eyes retract into 

 a normal position, the cartilaginous rod becoming folded upon itself 

 into a tangled mass in the orbit (Figs. 391-2). 



THE MIGRATORY EYE 



This is a curious phenomenon seen in the many types of flat-fishes. 

 In the Selachians which are compressed dorso-ventrally, the two eyes 

 migrate equally towards the dorsal mid-line so that they are directed 

 more or less skywards. The flat Teleosteans (which include such food- 

 lishes as halibut, plaice, turbot and sole) when young have the normal 

 t<rrnedo -shaped body of a fish and they swim with the usual 

 oj; tation with laterally directed eyes ; but at a later stage when 



