SENSE ORGANS. 



FlG. 70. Gran- 

 dry's corpuscle, 

 after Bohm and 

 Davidoff. n, axis 

 cylinder of nerve. 



FIG. 71. Pa- 



cinian corpuscle. 

 ;/, axis cylinder of 

 nerve. 



birds, two or more biscuit-shaped 



cells are included in a connec- 

 tive tissue, while the connecting 



nerve becomes flattened out into 



disks between each two cells. A 



more complicated type is found 



in the corpuscles of Vater or 



Pacini, elliptical structures 



composed of layers of cells like 



the layers of an onion, into the 



centre of which projects the 



axis cylinder of a sensory nerve. 



Under the heading of tactile cor- 

 puscles (Wagner's or Meissner's corpuscles) are 

 included club-shaped aggregations of cells, around which are 

 coiled the terminal nbrillae of a nerve. These last are scattered 

 all over the body in the amphibia, but are more restricted in 

 their distribution in the higher 

 groups. 



Among tactile organs must also 

 be enumerated the long facial hairs 

 (vibrissae) of mammals, the base of 

 each being surrounded by a network 

 of nerves. Besides these special 

 tactile organs there are numerous 

 free nerve terminations in the epi- 

 dermis of all vertebrates from cyclo- 

 stomes to mammals to which sensory 

 functions must be ascribed. 



The ears in all vertebrates are 

 paired structures on either side of 

 the head between the seventh and 

 ninth nerves. In the most highly 

 developed ears three portions are to 

 be distinguished, inner, middle, 

 and outer, the first of which only 

 is sensory and essential, and is the 

 only part occurring in the fishes ; 



FlG. 72. Meissner's corpuscle 

 from human finger, after Law- 

 dowski from Wiedersheim. a, 

 fibrous tissue envelope; b, cor- 

 puscle with its cells; , entering 

 medullated nerves ; n' ', ramifica- 

 tions of nerves ; ", club-shaped 

 nerve terminations. 



