ORIGIN AND STRUCTURE OF THE HEAD 



37 



Archencephalon and deuterencephalon. — The Craniate brain 

 is composed then of two parts of different origin, the first 

 being the epichordal part wiiich represents nothing else but the 



Fig. 13 Diagrams of the development of the Craniate 

 brain. 



A archencephalon, en neurenteric canal, civ 

 chiasma, D deuterencephalon, ek ectoderm, 

 en entoderm, / infundibulum. It lamina ter- 

 minalis, Af mesencephalon, Ms spinal chord, 

 nc notochord, np neuropore, P prosence- 

 phalon, pn processus neuroporicus, pr plica 

 rhombo-mesencephalica, pv plica ventralis. 

 /? rhombencephalon, r olfactory placode, ro 

 recessus opticus, tp tuberculum posterius. 



(after Kupffer, 1906. p. 13, 14). 



anterior, somewhat dilated, end of the former stomodaeum, 

 comparable to the brain vesicle of Amphioxus — which 

 consequently is not homologous to the brain of Craniates — 

 the other being that part of the prostomium which has been 

 folded in. In early ontogenetic stages a corresponding division 



