1 66 NERVOUS SYSTEM OF VERTEBRATES. 



epidermis. Each sense cell terminates at the surface by a rod- 

 like or hair-like projection which is much shorter than the 

 sense hairs of the neuromast organs. Since the taste organs are 

 stimulated by chemical changes they do not need the long sense 

 hairs which adapt the neuromasts to stimulation by vibrations 

 in fluids. Beneath the organ nerve fibers penetrate the dermis, 

 lose their sheaths and end by fine branches in contact with the 

 sense cells. A more intimate union between the cells and terminal 

 branches of the fibers has not been seen. To facilitate comparison 

 between neuromasts and taste organs there are shown in Fig. 85 

 two taste organs and two neuromasts from the same embr}^o of a 

 bony fish. The tall form of taste organ is taken from the lining 

 of one of the^gilFarches and represents the pre^•ailing form in the 



Fig. 86. — A taste organ from the^'phan-nx of the ammocoetes of Petromyzon 

 dor sat us. 



pharynx, where the organs are best developed. The lower organ 

 is taken from the oesophagus near the opening of the duct of the 

 smm bladder and is of the same form as those in the mouth. 

 The sharp contrast between the sense cells in these and in the 

 neuromasts requires no comment. In Fig. 86 is drawn a taste 

 organ from the pharynx of the larva of a cyclostome and in Fig. 

 87 a taste organ from the skin of an adult of another species. The 

 great difference in form of the two organs suggests a profound 

 influence of the surrounding structures, but both organs have 

 the same type of sense cells as are in the taste organs of all verte- 

 brates. 



The innervation of the taste organs is as follows. Those in 

 the pharynx are innervated by the visceral branches of the vagus 



