292 GLOSSARY OF EMBRYOLOGICAL TERMS 



mon nervous and enteric chamber of Amphioxus; the Kupffer's vesicle 

 of fish embryo; possibly the primitive pit of chick embryo. (Syn., 

 notochordal canal, primitive pit.) 



Neuroblasts — primitive or formative nerve cells, probably derived (along 

 with epithelial and glia cells) from germinal cells of embryonic neural 

 tube. 



Neurocoel — cavity of neural tube, formed simultaneously with closure of 

 neural folds. (Syn., central canal, neural canal.) 



Neurocranium — dorsal portion of skull associated with brain and sense 

 organs. 



Neuroglia — see Glia Cells. 



Neuropore — temporary opening into neural canal due to a lag in fusion of 

 neural folds at anterior extremity; permanent in Amphioxus and in 

 vicinity of epiphysis of higher vertebrates. 



Neurula — stage in embryonic development which follows gastrulation and 

 during which neural axis is formed and histogenesis proceeds rapidly. 

 Notochord and neural plate are already differentiated, and basic verte- 

 brate pattern is indicated, 



Notochord — rod of vacuolated cells representing axis of all vertebrates, 

 found beneath neural tube and dorsal to archenteron. Thought to be 

 derived from or simultaneously with endoderm. 



Notochordal Sheath — double mesodermal sheath around notochord consist- 

 ing of an outer elastic sheath developed from superficial chorda cells 

 and an inner secondary or fibrous sheath from chorda epithelium. 



Nucleolus — the body generally within the nucleus which has no affinity for 

 chromatin dyes, but stains with acid or cytoplasmic dyes. Function un- 

 known. (Syn., plasmosome.) 



Oesophagus — elongated portion of foregut between future glottis and 

 opening of bile duct of frog embryo; temporarily occluded just behind 

 glottis but opens again. 



Olfactory Lobes — anterior extremities of telencephalic cerebral lobes, 

 partially constricted, associated with first pair of cranial nerves. 



Olfactory Pit — depressions within olfactory placodes of 6 mm. frog embryo 

 which will become olfactory organs (external nares). 



Olfactory Placode — thickened ectoderm lateral to stomodeal region found 

 in 5 mm. frog embryo, primordia of olfactory pits. 



"Omne Vivum e Vivo" — all life is derived from preexisting life (Pasteur). 



