No. I.] SEA'SE-ORGANS OF LUMBRICUS AGRICOLA. 209 



The nerve-fibres proceeding from the sense-cells are readily 

 distinguishable from those which supply the epidermis. They 

 are smaller in diameter and consequently of more delicate 

 appearance ; in their course along the base of the epidermis 

 they neither branch nor anastomose, but pass directly to the 



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^vc. 





a.--- 



^''mts. ie{t, 



\at\t. rvr. 



Fig. I. A diagram showing a ventral ganglion and the course of its three pairs of nerves. In 

 this diagram the ventral ganglion is represented in place and the body wall cut through on one side 

 to show the nerves, aiit. nr., anterior nerve-trunk ; a, space into which the ventral rami pass (this 

 space is between the ventral longitudinal muscle-tract and the inner intcrsetal tract ; cir. vius., cir- 

 cular muscle-layer; cut., cuticula ; d. r., dorsal ramus of nerve; dor. loti. tr., dorsal longitudinal 

 muscle-tract ; <?/., epidermis ; ep. nr., epidermal nerve ; mt. Ion. tr., inner intersetal tract of longi- 

 tudinal muscles ; int. long. tr. 2, outer intersetal tract ; intra./., intraepidermal nerve-fibres ; ints. 

 jfr., intersegmental groove ; /«/^. i(?/., intersegmental septam ; lat. Ion. tr., lateral tract of longi- 

 tudinal muscles; m. ^r., median groove around metamere , m. h»-., median nerve-trui# (anterior 

 nerve of so-called " double root ") ; nr. r., nerve-ring ; sen. org., sense-organ ; sub. n., subepidermal 

 network ; ven. gan., ventral ganglion ; ven. Ion. tr., ventral longitudinal tract ; v. r., ventral ramus 

 of nerve. 



nearest one of the epidermal nerves which traverse the circular 

 muscle-layer ; the sensory fibres from sense-organs on one side 

 of a metamere always enter an epidermal nerve of that side ; 

 they never cross the mid-dorsal or mid-ventral line. In these 

 nerves, the fibres from the sense-cells are never so deeply stained 

 as the efferent nerve-fibres, — they usually present a clear 

 brownish appearance. They are further distinguishable from 

 the fact that they keep more nearly parallel to one another and 

 run in uniformly sinuous lines. 



