346 



THE EYE IN EVOLUTION 



Amby stoma 



it bulges downwards into the roof of the month, thus forcing food down 

 the throat. 



The anuran orbit is large and membranous with considerable gaps 

 in its walls and without an interorbital septum or any division between 

 the two cavities. As we have seen, the orbital cavity opens directly 

 into the pharynx. 



THE URODELAN EYE 



MANY OF THE TAILED AMPHIBIANS, witli their cavcrnicolous and 

 secretive habits, have reduced or degenerate eyes ^ ; even those types 

 which are visually active, such as the salamanders and newts {Sala- 

 niandra, Triturus) and Axolotl (the larva of the salamander, Amhy- 

 stonia tigrinum), have eyes which are smaller and simpler than those of 

 Anurans although designed on the general amphibian plan (see Okajima, 

 1909 ; Rochon-Duvigneaud, 1943). The main differences are the 



Fig. 411. — The Head of the Newt, Triturus. 



Fig. 412. — The Axolotl, larva of Ambystoma tigrjxum (Zool. Soc, 



London). 



1 p. 726. 



