kand: kervous system of lumbricid^. 117 



plished. According to Hescheler the alimentary canal grows forward to 

 meet a stomodseum or invagination of the epidermis, and the opening 

 to the exterior is effected by a rupturing of the epithelial and epider- 

 mal layers, the epidermal invagination becoming the mouth cavity and 

 the region posterior to the point of rupture becoming the pharynx. In 

 the preparation from which Figure 16 is taken, the epidermal invagina- 

 tion has progressed to meet the alimentary epithelium. In some sec- 

 tions a delicate layer of the epithelium was found still closing the end 

 of the canal (see Figure 16). In other sections this layer was brolien 

 away, probably accidentally. 



As to the nervous system, Figure 16 represents a much more advanced 

 stage of regeneration than Figure 15. In this advanced stage the end 

 of the old cord is as sharply marked as ever. The new fibre tract has 

 extended forward to encircle the alimentary canal, the two branches 

 uniting in a small mass of cells {gn. su'oes.) above the stomodeal 

 invagination. This mass of cells constitutes a well-defined brain 

 fundament. 



After the condition of Figure 16 has been reached, we have to do 

 only with growth and segmentation of the parts already laid down. I 

 made no preparations of material regenerated more than forty days. 

 There is much individual variation as to the rapidity of the process. In 

 one animal after thirty-four days' regeneration the brain was scarcely 

 smaller than in the normal worm and had come to occupy its position 

 in the third segment. The number of segments regenerated in this case 

 could not be determined. The brain and anterior end of the ventral 

 cord in this animal could hardly be distinguished from those of a nor- 

 mal worm except for the occurrence of numerous dividing cells at the 

 anterior tip of the cord and in the posterior dorsal region of the brain. 

 The sheaths enclosing the new nervous parts were well developed. But 

 in most of the worms, after thirty-five to forty days' regeneration, the 

 regeneration of the nervous parts had not reached so advanced a 

 stage. 



The foregoing statements are sufficient to give a general outline of 

 the process of regeneration. Hescheler ('98) has described the process 

 in more detail j as far as my observations go, my results agree with his. 

 I now propose to discuss the origin of the new nervous parts more 

 minutely. 



