CRANIAL GANGLIA IN AMPH1OXUS. 



117 



Sections by the rapid Golgi method 

 show these cells and confirm the descrip- 

 tion given above. Cells of the following 

 types are seen to send fibers into the 

 dorsal roots. In the figures the several 

 types are indicated by the arabic numerals 

 which are used here in the text, (i) 

 Bipolar cells near to or extending across 

 the middle line of the cord, whose cen- 

 tral processes go to the further side of 

 the cord from the roots which the peri- 

 pheral processes enter. The central pro- 

 cess after reaching the opposite side of 

 the cord either (a) enters the dorsal 

 bundles without dividing, (b) divides in 

 T- or Y-form into rostral and caudal 

 branches, or (c] ramifies at once more or 

 less profusely. The last mode of be- 

 havior is seen most often in my prepara- 

 tions. These cells mingle with the more 

 centrally situated cells of the next type. 

 (2) Bipolar cells within the cord more or 

 less radially placed with reference to the 

 nerve root, whose central processes 

 remain on the same side of the cord as 

 the roots which the peripheral processes 

 enter. These cells may be situated any- 

 where within the area of a fan whose 

 handle is represented by the nerve root 

 and whose rays are represented by these 

 cells and their processes. The bodies 

 of the cells are situated among the 

 bundles of root fibers as they turn for- 



FIG. I . A horizontal section of the nerve cord and 

 dorsal roots. The parts above and below the dotted 

 lines were drawn from adjacent sections of the same 

 animal. The arabic numerals indicate the types of 

 cells described in the text. A', longitudinal bipolar 

 cell of Retzius. The smaller dorsal ramus of each 

 nerve diverges caudally from the larger ventral ramus. 



