240 METAZOAN PHYLA 



pharyngeal ganglia, is often given the term brain (Fig. 138). However, 

 these ganglia apparently do not function in any way different from the 

 other ganglia of the body. Their size is due in part to the greater area 

 from which they receive afferent impulses and to which they distribute 

 efferent impulses and in part to the fact that they innervate the most 

 sensitive part of the body. Either an increase in the area served and 

 the number of structures involved or an increased sensitiveness of the 

 parts means an increase in the number of neurons in any nerve center 

 and therefore an increase in size. The ganglia in question do not possess 

 two attributes which are associated with the brains of higher animals. 

 They do not exercise that dominance over the functions of the body 

 generally that a true brain should and may be removed and regenerated 

 with the rest of the anterior end of an earthworm. It is better, therefore, 

 to avoid the use of the word brain in connection with this type and with 

 other invertebrates with a nervous system of this character. 



