188 NERVOUS SYSTEM. 



the nervous system is most developed in that part of the 

 body. There is generally in these wheel-animalcules, as in 

 the hydatina (Fig. 82. B,) a distinct supra-oesophageal gan- 

 glion (a,) with smaller lateral ganglia (b, c 9 ) surrounding the 

 entrance of the alimentary canal (e) ; and from the anterior 

 or inferior ganglia (c, c,) proceed the nervous columns back- 

 wards along the ventral surface of the trunk (d.) These ab- 

 dominal nervous columns, as in the entozoa, are sometimes 

 approximated to each other, and without perceptible ganglia 

 in their course, and in others they are separated to a greater 

 or less distance from each other, and have numerous ganglia 

 developed along their sensitive columns. In the hydatina, 

 the longitudinal nervous columns are united (82. B. d 9 ) and 

 without apparent ganglia below the alimentary canal. In the 

 diglena lacustris the nervous columns are a little separated 

 from each other, and present only one pair of ganglia imme- 

 diately below the oesophagus, and another pair below the 

 pyloric extremity of the stomach. The longitudinal ventral 

 columns are much more separated from each other, in their 

 whole course, in the notommata clavulata, and each of these 

 lateral chords presents nine perceptible ganglia, in its course 

 backwards to the posterior extremity of the trunk. These 

 abdominal ganglia are symmetrically disposed in pairs, 

 though removed laterally to a distance from each other on the 

 inferior part of the trunk. 



The nervous system of the cirrhopods (Fig. 82. C,) is 

 symmetrically disposed in approximated columns (b, c 9 ) 

 along the abdominal surface of the trunk, with parallel pairs 

 of ganglia regularly developed along their course, as in all 

 the higher articulated classes. In the anitifa (Fig. 82. C,) 

 we perceive a slender white nervous ring surrounding the 

 oesophagus (a,) and sending out small filaments to the neigh- 

 bouring parts, but scarcely forming a perceptible supra- 

 ossophageal ganglion, from the imperfect development of the 

 sensitive and masticating apparatus in these fixed and in- 

 verted testaceous or entomostracous animals. As the long, 

 jointed and ciliated feet, with their thick muscular haunches, 

 and supporting the branchiee at their base, are developed 

 from the sides of the posterior part of the trunk, the ganglia, 

 like the nervous columns which connect them, are large in 

 that part of the body, and correspond in position with the 

 origin of the several pairs of legs (b, c, d, e, /.) So that 



