272 GLOSSARY OF EMBRYOLOGICAL TERMS 



Cytolysis — breakdown of cell indicated by dispersal of formed compo- 

 nents. 



Cytoplasm — material of cell exclusive of nucleus; protoplasm apart from 

 nucleoplasm. 



Delamination — separation (of cell layers) by splitting, a process in meso- 

 derm formation. 



Dermal Bones — bony plates which originate in dermis and cover cartilag- 

 inous skull. 



Dermatome — outer unthickened wall of somite which gives rise to dermis. 

 (Syn., cutis plate.) 



Dermis — deeper layers of skin entirely derived from mesoderm (derma- 

 tome). 



Dermocranium — portion of skull which does not go through an intermedi- 

 ate cartilaginous stage in development. (Syn., membranocranium.) 



Determination — process of development indicated when a tissue, whether 

 treated as an isolated unit or as a transplant, still develops in the 

 originally predicted manner. 



Determination of Sex — mechanism by which realization of sex differences 

 is achieved, generally thought to be associated with chromosomal 

 relations. 



Deutencephalon — caudal region of brain which later forms mesencephalon 

 and rhombencephalon. 



Deutoplasm — yolk or secondary food substances of egg; non-living. 



Development — gradual transformation of dependent differentiation into 

 self-differentiation; transformation of invisible multiplicity into a 

 visible mosaic elaboration of components in successive spatial hier- 

 archies. 



Development, Mosaic — "all the single primordia stand side by side, sepa- 

 rate from each other like the stones of a mosaic work, and develop 

 independently although in perfect harmony with each other, into the 

 finished organism" (Spemann, 1938). Some believe there is pre- 

 localization of embryonic potencies within egg, test for which would 

 be self-differentiation. 



Development, Regulative — type of development requiring organizer or in- 

 ductor influences since each of the early blastomeres could develop 

 into whole embryos. Structures are progressively determined through 

 action of evocators. 



