THE DEVELOPMENT OP LEPIDOSIEEN PARADOXA. 459 



Fig. 12.— Illustrating tbe development of tlie motor nerve-trunks. All 

 three figures represent portions of sections perpendicular to the longitudinal 

 axis of the body. 



ad. Arcliiuephric duct ; me. Mesenchyme cells; m.ii.r. Motor uerve- 

 truuk; mi/. Myotome; ii.c. Neural tube; >i. JN'otocliord ; scl. 

 Sclerolome. 



A. Stage 21'. Zl'Iss A, oc. i. Section of an embryo excised from the 



egg and flattened out, so as to slighlly separate myotome and 

 spinal cord, and display the rudiment of the nerve-trunk which 

 even at this stage unites the two. 



B. Stage 27. Zeiss D, oc. 2. The myotome has become separated 



from the neural tube by interposed mesenchyme. The nerve- 

 trunk is lengthened out, and externally is continued into the 

 muscle-cells of the myotome. 

 c. Stage 29 + . Zeiss D, oc. 2. Tne nerve-trunk is now ensheathed 

 in mesenchymatous protoplasm cont;iining nuclei and yolk 

 granules. 



