170 



PRACTICAL ZOOLOGY 



out of its burrow, may be answered at the same time. If a 

 worm be drawn through the fingers from the front backwards, 

 it will feel smooth to the touch, but if drawn from the back for- 

 wards, it will feel rough. This is due to the presence of strong, 



dorv.r 



neph 



TUphrost 



n.co 



FIG. 97. Diagram of a cross section of an earthworm. 



circ.mus, circular muscle fibers ; coel, cselom ; dors.v, dorsal vessel ; epid, 

 epidermis ; ext.neph, nephridiopore ; hep, chlorogogen cells ; long.mus, longi- 

 tudinal muscles; neph, nephridium; nephrost, nephrostome; n.co, nerve- 

 cord; set, setae; sub.n.vess, subneural vessel; typh, typhlosole; vent.v, 

 ventral vessel. (From Marshall and Hurst.) 



sharp bristles, the setae, which extend obliquely backward from 

 the sides and under part of the body (Fig. 97, set). There are 

 four pairs of these setae in each segment, and they may be moved 

 by sets of muscles situated just within the body wall. They 

 are moved from behind forward like legs and are of special serv- 



