542 THE SENSORIAL FUNCTIONS. 



its functions would be conveyed by calling it the 

 principal brain, and considering the other ganglia 

 as subordinate brains. This large ganglion, which 

 supplies an abundance of nervous filaments to 

 every part of the head, seems to be the chief 

 organ of the higher senses of vision, of hearing, 

 of taste, and of smell, and to be instrumental in 

 combining their impressions, so as to constitute 

 an individual percipient animal, endowed with 

 those active powers which are suited to its rank 

 in the scale of being. 



Such is the general form of the nervous system 

 in all the Annelida ; but in the higher orders of 

 Articulata we find it exhibiting various degrees 

 of concentration. The progress of this concen- 

 tration is most distinctly traced in the Crustacea* 

 One of the simplest forms of these organs occurs 

 in a little animal of this class, which is often 

 found in immense numbers, spread over tracts of 

 sand on the sea shore, and which is called the 

 "^^^^^^^arimsKsasiiite. Talitrus locusta, or Sand-hopper, 

 (Fig. 438). The central parts of 

 its nervous system are seen in 

 Fig. 439, which represents the abdominal side 

 of this animal laid open, and magnified to twice 

 the natural size. The two primary nervous 

 cords, which run in a longitudinal direction, are 



* See the account of the researches of Victor Audouin, and 

 H. M. Edwards, on this subject, given in the Annales des 

 Sciences Naturelles; xix. 181. 



