Nervous Systems 811 



mental nerves, containing both sensory and motor fibers, which connect with 

 the subepidermal plexus. Can this peripheral network conduct impulses along 

 the body? Can a strip of earthworm body wall move spontaneously? Are 

 epidermal sense cells connected through the peripheral network directly to 

 muscles? 



It has long been known that if the ventral nerve cord is cut or is removed 

 from the earthworm for several segments, peristaltic waves still pass from 

 one end of the worm to the other. Peristaltic transmission occurs if the two 

 pieces of a transected worm are connected by a thread or when a few seg- 

 ments are anesthetized.^'*" If part of the nerve cord is removed, a wave of 

 mucus secretion fails to pass from normal to denervated segments.^"* If the 

 nerve cord is removed from more than three segments and those segments are 

 firmly pinned down so that no pull can be exerted beyond them, no peris- 

 taltic wave passes, but if fewer than three segments are denervated and 

 these segments pinned down, a wave is conducted. •*■'*' Action potentials in 

 the segmental nerves show that each nerve serves three segments, the different 

 nerves serving overlapping fields which are fairly discrete. When one nerve 

 is stimulated there is contraction in its own segment and, to a less extent, in 

 adjacent segments.^'*'' When a T-shaped cut is made in the lateral body 

 wall of an earthworm, transmission of a contraction wave occurs "around 

 the corner" if the nerve cord is intact, but not when the nerve cord is lack- 



Spontaneous contractions have been seen in strips of earthworm body 

 wall lacking the ventral nerve cord and have been denied. ^^^ Janzen^^** ob- 

 tained spontaneous periodic contractions in strips of earthworm body wall 

 which had been narcotized during dissection, but not in non-narcotized 

 strips; the contractions were usually local but could be propagated; the two 

 muscle layers could contract separately. Hatai^'^'^ reported spontaneous activ- 

 ity in dorsal strips from the posterior end of Alloloho'phora, but not from 

 the anterior portion, and not at all from Perichaeta. When dorsal pieces are 

 isolated in Lumhricus the muscles of segments anterior to and including the 

 clitellum often contract at the edges for hours after excision, this probably 

 being a response of the muscle to injury; these excised^ segments fail to show 

 spontaneous movements. Postclitellar strips relax but are not spontaneously 

 active. Dorsal strips consisting of about twenty extreme posterior segments, 

 however, sometimes show spontaneous contractions.^-" It appears then that 

 posterior regions of the dorsal body wall of earthworms are capable of spon- 

 taneous movement and that contractions can occur in conducted waves, but 

 there is no reason to implicate the subepidermal plexus. Conduction may be 

 from muscle cell to cell as in vertebrate smooth muscle. The body wall muscle 

 may, like the smooth muscle of the mammalian intestine, be capable of 

 some intrinsic movement. 



Janzen^^^ found that tactile stimulation of dorsal body strips elicited con- 

 tractions, usually local but sometimes propagated; spontaneously active 

 strips showed the best responses. The body wall muscle may be responding 

 to direct stimulation, f^owever, in a few of the preparations from the posterior 

 end of Lumhricus a clear-cut response to bright illumination was obtained 

 after dark-adaptation.^^'^ It is probable that in the response to illumination 

 and to very light touch there is some direct connection between sense end- 



