The Reactions of the Vertebrate Embryo to Stimulation etc. 579 



Explanation of Figures\ 



B. Protoplaamic Strands (bridges, plasmodesmata) uniting Spinai Cord 



and Myotome. 

 Spinai Ganglion cell. 

 Central canal. 

 Commissural tracts. 

 Epidermis. 

 Lateral hörn. 

 Myotome. 



Ramus n. ventralis spinalis. 

 Process of giant ganglion celi. 

 Plexus. 



Primitive fibril Splitting up into finer filaments within the cord. 

 Spinai cord. 

 Ventral roots. 



Piate 23. 



Fig. 1. Pristiurus melanostormis length 4,5 mm. Protoplasmic bridge (plas- 

 modesma) extending from spinai cord to myotome. (Bausch and Lomb 

 homog. immers. Vi2 oc. 2.) 



Fig. 2. Pristiurus melanostomus length 5 mm. Bridge connecting cord and 

 myotome. Primitive neurofibril embedded in matrix of latter. (Same 

 magnification as in Fig. 1.) 



Fig. 3. Pristiurus melanostomus length 5 mm. a) Large celi in region of 

 ventral horn with well developed apical process. The black granules 

 are probably the transverse sections of neurofibrils. A single fibril 

 may be seen near apex of process. b) Bündle of fibrils just be- 

 ginning to split up longitudinally. (Zeiss apochromat. obj. 2 mm. 

 oc. 12.) 



Fig. 4. Scyllium eanicula length 6 mm. Giant (Beard) Celi connected with 

 process of spongioblast {p] by bündle of fibrils (p*), with others (p*) 

 running forward in direction of ventral roots. At p^ a bündle directed 

 inwards, but ending abruptly before reaching spongioblast. A fourth 

 bündle passing outwards and as seen in succeeding sections has 

 almost reached inner surface of epidermal layer. (Zeiss apochrom. 

 obj. 2 mm. co. 12.) 



Fig. 5. Torpedo ocellata length 7 mm. e ventral root. d portion of proto- 

 plasm forming apical process which does not contain any fibrils. 



* Unfortunately it is not possible to give the exact magnifications of the 

 sections represented by the drawings. Figures 14 and 15 were drawn at the 

 level of the table, on which the microscope stood, and the others in the 

 same piane as the upper surface of a drawing-table of about 14 cm. in 

 height. 



