158 A. B. DAWSON 



scribes, however, two types of bipolar cells which are distin- 

 guished from one another by the differences in their size and in 

 the arrangement of their neurofibrils. The smaller cells were 

 referred to merely as ^die Nervenzellen' and contained neuro- 

 fibrils which, although often highly branched, transverse d the 

 cell bodies without anastomosing. The large bipolar cells, on 

 the other hand, showed the intracellular fibrils anastomosing to 

 form complex networks and were given the descriptive title, ' die 

 intermuskularen sensorischen Ganglienzellen.' The small cells 

 were observed on the inner side of the nerve ring close to the longi- 

 tudinal muscles and in the margin of the ventral nerve cord at the 

 point of exit of a lateral trunk. Boule ('13) also shows small 

 bipolar cells in the latter position (fig. 13). Of the large bipolar 

 cells, some were situated in the nerve ring, while others lay en- 

 tirely within the circular muscle layer. 



MATERIAL AND METHODS 



Helodrilus caliginosus and AUolobophora (Eisenia) foetida, 

 readily obtained in any market garden, were utilized in this 

 work. All the material studied was taken from the midbody 

 region, somewhat posterior to the clitellum. Very satisfactory 

 preparations were obtained with intra vitam methylene-blue stain- 

 ing and Boule's modification of the Ramon y Cajal technique for 

 neurofibrils. Intravitam methylene-blue staining was secured 

 by means of two methods. Some animals were injected intra- 

 coelomically with a 1 per cent solution of methylene blue in nor- 

 mal saline. Others were partially immersed in the solution and 

 allowed to remain in the fluid till they became colored a deep 

 blue. In both cases the color was fixed with Bethe's invertebrate 

 fluid and the tissue imbedded in paraffin and cut in serial sections 

 20 M thick. 



For silver impregnation, portions of worms, 5 to 10 mm. long, 

 were fixed in one of Boule's mixtures, usually formula B (for- 

 malin, 25 cc; glacial acetic acid, 5 cc; ammonia, 0.5 cc; distilled 

 water, 100 cc), for from twenty-four to forty-eight hours/ im- 

 pregnated six days in a 1^ per cent silver-nitrate solution at 38°C. 



