2l8 



Journal of Comparative Neurology. 



In such a budding segment the central nervous system 

 consists, at the beginning of the process, of the ventral nerve 

 cord with the segmental ganglia. The cord is made up of a cen- 

 tral fibrous mass, surrounded in the ganglionic region by cells. 

 These cells are more numerous on the ventral surface and on 

 the lateral horns of the cord. (Figs, i, 2, gn. v.) 



In the budding zone the ectoderm thickens, forming a 

 girdle about the middle of the segment. Cell proliferations of 



J't^. I. (Diagrammatic). Transverse section of Dero vaga before budding 

 process begins. cl. I. In., cells of the lateral line ; con't. crc'a:., circumcesopha- 

 geal commissure; fhr. cols., giant fibers; gn. </., brain; f;n. v., sub-oesopliageal 

 ganglion; mu. d., dorsal longitudinal muscle band ; mu. d\, detached portion 

 of dorsal band; mu. /., lateral muscle band; mu. v., ventral muscle; mu. v\, 

 detached portion of ventral band; neph., nephridium ; phy., pharynx; set. v., 

 ventral bristle bundle; vas. sng., blood vessel; /, 2,^, regions where the ecto- 

 derm gives rise to nervous elements. 



ectoderm break through the peritoneal lining, penetrating the 

 muscular layers, into the body cavity. If we call the band of 

 longitudinal muscle fibers dorsal to the lateral line cells (Figs, i 



