116 , NERVE CENTKES. 



the nervous system, in the higher invertebrata and in the verte- 

 brata it is probable that the nerve tissue collected in the nerve 

 centres exceeds in amount that spread out amongst the tissues 

 in all the other parts of the organism. 



" Each central nerve cell consists of a mass of bioplasm sur- 

 rounded by formed material, which last is drawn off at two or 

 more points into fine threads. These divide and subdivide into 

 still finer ones at a short distance from the cell, and are, in fact, 

 processes of the nerve cell which become nerve fibres" The 

 processes invariably take opposite directions soon after they 

 have left the "cell." In vertebrata there are two principal 

 kinds of central nerve cells which are very distinct from one 

 another, and probably differ in function not less than they do 

 in structure. These are, 



1. The angular, or caudate nerve cells. 



2. The oval, pyriform, or spherical nerve cells ("Biopl.," p. 186). 

 The latter alone are considered to be centres of evolution of 



nerve force, while the caudate cells are merely commissural 

 organs. Dr. Beale denies the existence of apolar or unipolar 

 cells, and maintains that there are at least two fibres to every 

 nerve cell. 



The spherical, oval, and pyriform nerve cells are composed 

 of masses of protoplasm, from which two or more fibres appear 

 as if drawn out, and are curved and coiled as if they continued 

 to grow, or were spun off as the cell revolved. These cells are 

 found in all the ganglia of the sympathetic, and on the posterior 

 roots of the spinal nerves, the gasserian ganglia, &c. In some 

 ganglia cells there is a straight and a spiral fibre. A singular 

 ganglion cell has been described by J. Arnold, but several 

 German authors have doubted the authenticity of Beale's pyri- 

 form ganglia, the drawing of which is copied in most text- 

 books. The actual specimen has, however, been shown to 

 many observers under the 1-25 (1800 diam.) Among the rest 

 I have seen it, and can testify to the correctness of the drawing, 

 and to the impossibility of such an appearance being produced 

 by any accidental tearing out of connective tissue or any such 

 cause. Dr. Beale concludes that these spherical, oval, and pyri- 

 form cells are the sources of nervous power, while the caudate 



