THE CAUSAL PARASITE. 



29 



than broad, about 10 by 7 (x. The thick walls inclose a small lumen 

 which can be expanded and contracted by the muscular action, thus 

 acting in the manner of a pump in connection with the esophagus 

 and spear (fig. 3). The expansion and contraction of the bulb are 

 often synchronous vnih. motions of 

 the spear. Immediately behind the 

 bulb the alimentary canal is rather 

 narrow for a very short distance and 

 then widens out rather abruptly into 

 the comparatively thick-walled di- 

 gestive portion which fdls the body 



X 700 



Fig. 2.— .^terior portion of the same nematode 

 sho^vn in figure 1: a, Anterior end; h and c, free 

 and inclosed portions, respectively, of spear; d, 

 esophagus; e, outer wall, and, /, central portion 

 of esophageal bulb; g, nerve ring; h, second 

 bulb; i, tliickened wall of alimentarj' canal; 

 ;, excretory pore; fc, gland. Magnified 700 

 diameters. Drawn by W. E. Chambers. 

 Fig. 3. — Larva of Heterodera radicicoh: a, An- 

 terior end; 6, c, and «, spear ;<?, buccal cavity; cavity and continues unchanged to a 

 /, esophagus; J and A, outer and inner por- „'j.Vii -• . ,i 



tions, respectively, of esophageal bulb; i, P^^^* shortly anterior to the aUUS. 

 nerve ring; ;, excretory pore; k and 1, lumen The anterior part of this digestive por- 

 and thick wall, respectively, of alimentary , • • j. i i i i n. 



canal; m, fat globule (?); n, anus; o, pos- ^^^^ ^^ not clcarly marked ofl aS a 

 terior extremity. Magnified 700 diameters. SCCOnd bulb, as is the CasC in SOmS 

 Drawn by W. E. Chambers. . c m i i t t ■, 



species ot iylenchus. immediately 

 behind the esophageal bulb, surrounding the short, narrow portion of 

 the canal, can be seen occasionally the nerve ring. About 25 to 40 fi 

 anterior to the anus the walls begin to become thicker and the canal 

 tapers, the anal opening itself being rather small. 



217 



