302 



THE EARTHWORM AND OTHER ANNULATA 



ist may still be used as an introduction to the behavior of the 

 earthworm from the standpoint of the animal's activities under 

 natural conditions. 



Regarding the sense of touch, the whole body is very sensitive 

 to mechanical contacts, as one may see by touching the animal at 

 different places. Even a slight puff of air from the mouth may 

 cause an instant withdrawal into the burrow. In general, the 

 anterior region is the most sensitive, then the posterior, and the 

 middle of the body least of all, as might be suspected from the 





n 



Fig. 145. Fig. 146. 



Fig. 145.— Epidermis of earthworm, showing the columnar epithehal cells, 

 gland cells, and sensory cells of a sense organ. 



b.m., basement membrane; c, cuticle; c.c, one of the columnar epithelial cells that 

 form sheath of sense-organs; g.c, gland cell with secretion being exuded from pore in 

 cuticle; ep.c, epithehal cell; s.c, sensory cells (receptors) with outer ends protruding 

 through openings in cuticle and inner ends prolonged as sensory fibers; s./., sensory fibers 

 or axons arising from sensory cells (c/. Fig. 144). 



Fig. 146. — Light-perceiving cell in epidermis of earthworm. 



b.m., basement membrane; c, cuticle; I, lenshke body in cell; n, nucleus; o.n., 

 nerve fiber from base of cell (c/. Fig. 145. s /. ) ; r, retinella or retina-like structure 

 surrounding lens; s, sub-epidermal plexus of nerve fibrils. (After Hess, Jour, of Morph. 

 and Phtjsiol., Vol. 41 ) 



uses of these parts and their supply of sense-organs (Fig. 145). 

 The prostomium appears to be the most sensitive portion of the 

 animal. For example, when the worms first come out of their 

 burrows in the evening they make exploratory movements in all 

 directions, using the anterior end, and particularly the prosto- 

 mium, as an organ of touch. In a similar manner, leaves and other 

 objects that ai-e used as food may be subjected to a preliminary 

 examination by the prostomium. 



Something that may be described as a sense of taste exists, since 



