238 PHYLUM ANNELIDA. 
supra-cesophageal) ganglia are connected with the most 
anterior (or sub-cesophageal) pair on the ventral chain, by 
a narrow nerve-ring surrounding the beginning of the gut. 
The sub-cesophageal ganglia represent about five pairs of 
ganglia fused together. From the dorsal ganglia nerves 
proceed to the “eyes” and anterior sense spots ; from the 
ventral centres the general body is innervated. Special 
Fic. 122.—Transverve section of leech.—After Bourne. 
c., Cuticle; ¢., epidermis; c.7., dermis and outer muscles (circular 
and oblique); 2.., longitudinal muscles (the peculiar connective 
tissue is hardly indicated); ».#., radial muscles; Zv., lateral 
blood vessel; d@.s., dorsal sinus; vs., ventral sinus enclosing 
nerve-cord (x.); g., median part of crop, with lateral pockets (.)3 
z., testis ; £, nephridial funnels; v.@., vas deferens. 
nerves from the dorsal ganglia supply the alimentary canal, 
forming what is called a visceral system. 
The sense organs of the leech are ten so-called “ eyes,” 
besides numerous sense spots usually occurring on every 
fifth skin-ring. The eyes are arranged round the edge of 
the mouth, and look like little black spots. Microscopic 
<xamination shows them to be definite cups, surrounded by 
