S4 



GEXERAI, TRIXCIPLES OF ZOOLOGY 



telegraph system. These are to lie 

 eonsiilered as the specihc element 

 of the nervous system. 



Ill the vertebrates the ganglion 

 ci;lls varv greatly in size; besides 

 small elements there are large cells, 

 only exceeded by the eggs in size, 

 which correspondingly ha\e large 

 nuclei recalling the germinal \esi- 

 cles. Unipolar, bipolar, and multi- 

 polar ganglion cells are recognized, 

 the tlifterences depending upon the 

 number of processes (nerve-tibres) 

 which arise. In multipolar cells 

 the number is large (fig. 52) and 

 they are of two kinds, dendrites and 

 axons or )ictirilcs. DtiiJrilcs are 

 so called because they branch again 

 and again, not far from their origin 

 from the cell. The axons (of which 

 there is usually Init one to a gang- 

 lion cell) can extend a long dis- 

 tance without gi\'ing off" liranches, 



except here and there side twigs {colhilvrals) which arise at right angles 



to the main tlbre; tliev often 



continue into peripheral 



nerves. They branch at their 



tips (It'hnfciulro) so the mor- 

 phological distinction from 



dendrites lies in the greater 



distance of the region of 



branching from the liody of 



the ganglion cell. In bijxilar 



ganglion cells Ijoth pirocesses 



appear as neurites, but if one 



is to be regarded as a dendrite 



with its branching at some 



distance from the cell, the 



definite physiological distinc- 



,• 1 . 1 • 1 1 ji t F'C.. ^^. — Motor !»an!i;lion cell from the thoracic 



tion has to f)e m\-oked that • ,■ ,, ■ i i <■ 1 , t, n l 



region ot the spinal cord of a dog (atler Belhe). 



the neurite carries the im- ", nucleus. 



Fio 



53. — Multipolar ganglion coll of man 

 Vafter Gegenbaur). j, a.\on. 



