CHAPTER 19 



THE EYES OF AMPHIBIANS 



This class includes the tailed amphibia — Urodela ; the tailless amphibia 

 — Anura ; the degraded blind and limbless amphibia — Apoda ; and the 

 extinct labyrinthodonts — Stegocephala . 



The pineal system of amphibians is particularly interesting on account 

 of the light that it sheds on intermediate stages between the more highly 

 evolved types of the parietal sense organ or pineal eye, such as is found 

 in the lampreys and lizards, and those types in which the end-organ fails 

 to develop and in which it appears that the proximal end only, grows and 

 becomes modified to form the epiphysis or pineal organ as in birds and 

 mammals. 



The Pineal System of the Urodela 



In this primitive order, which comprises the Tritons ; salamanders ; 

 the common British newts ; Amblystoma (Axolotyl) ; Amphiuma ; 



p , E P 



N.Ch 



Fig. 158. — Median Sagittal Section through the Head of an i8-mm. Larva 

 of Necturus macalatus, showing the Structures in the Parietal Region 

 of the Brain. (After C. S. Minot.) 



cp. : posterior commissure. 

 C. PI. : choroid plexus. 

 Ep. : epiphysis. 

 FB. : forebrain. 

 Hyp. : hypophysis. 



M. : mouth. 



MB. : midbrain. 



Op. Ch. : optic chiasma. 



P. A. : paraphysal arch. 



Par. : paraphysis. 



Necturus (Fig. 158) ; and Proteus, the pineal organ is very rudimentary 

 and in the adult lies entirely within the cranial cavity. The whole organ 

 consists at first of a flattened hollow vesicle, connected by a short 



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