THE PINEAL SYSTEM OF AMPHIBIA 



231 



the " pineal nerve." Whether the nerve-fibres are actually formed in 

 the stalk or grow into the stalk from neuro-sensory or ganglion cells in 

 the end vesicle is a problem which it is difficult to decide ; for, according 

 to the later publications of Ley dig (1891), the nerve-fibres do not actually 

 enter the vesicle as they appear to do in Fig. 164, but both nerves and 

 vessels pass beneath or around the vesicle and join a plexus of nerve- 

 fibres and capillary vessels in the surrounding connective tissue (Fig. 165). 



N. 



Fig. 164. 

 Another drawing of the same specimen as Fig. 165, showing pigment granules in 

 the epithelium of the wall of the frontal organ (Stieda) and the pineal nerve. 

 (After Leydig.) N. pin. : nervus pinealus. 



Fig. 165. — The Frontal Organ of Bombinator igneus (Stage of Two-legged 



Larva), seen from below. 



Surrounding the organ are blood-vessels and nerves. Three-branched pigment 

 cells of the connective tissue type are present, and sections of cutaneous 

 glands. N. pin. : nervus pinealis. 



(From a drawing by Leydig, 1891.) 



Moreover, neither fully differentiated neuro-sensory cells nor ganglion 

 cells have been described in the end vesicle, but on the contrary in most 

 cases the epithelium shows signs of degeneration and the nerve-fibres 



