GLOSSARY 



497 



YOLK PLUG - large yolk cells which are too 



large and sluggish to be immediately incor- 

 porated in the floor of the archenteron, 

 hence are found protruding slightly from 

 the mouth of the blastopore to form a plug 

 which is distinct by color from the surround- 

 ing pigmented marginal zone (amphibia). 



Term used as identification of a late stage 

 in gastrulation. 



ZONE, MARGINAL - presumptive chorda-meso- 

 dermal-endodermal complex at the junction 

 of the roof and the floor of the early gastrula. 

 Syn. , germ ring. 



NOTE: A glossary of some 350 terms in morphological embryology 

 may be found in the author's revised edition of "Laboratory 

 Manual of Vertebrate Embryology". (1961) 



"OMNE VIVUM EX OVO" 



HARVEY 



"OMNIS CELLULA E CELLULA" 



VIRCHOW 



