Reproduction 



259 



Fig. 213. Amphioxus. Transverse sections of embryos at successively later 

 stages, showing origin of notochord, neural tube, and mesoderm. (A) Section some- 

 what anterior to the middle of the length of an embryo slightly older than that 

 represented in Fig. 210D. (E) From embryo having two pairs of mesodermal 

 pouches. (G) Section near the middle of the length of an embryo having nine 

 pairs of mesodermal pouches, (a) Archenteron; (ec) ectoderm; (en) endoderm; 

 (mes) mesoderm; (nc) notochord; (np) neural plate; (nt) neural tube. (After 

 Cerfontaine. Courtesy, Neal and Rand: "Ghordate Anatomy," Philadelphia, The 

 Rlakiston Company.) 



