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GLOSSARY 



POTENCY, PASSIVE - potencies formed in the 

 presence of inductive forces only (Bautz- 

 mann, 1929). 



POTENCY, PROSPECTIVE - the sum total of 

 developmental possibilities, the full range 

 of developmental performance of which a 

 given area (or germ) is capable. Somehow 

 more than, and inclusive of, prospective 

 fate and prospective value. (See these 

 terms. ) Connotes possibility, not power. 

 Not to be confused with competence. 



POTENTIAL, MORPHOGENETJC - the strong 

 or weak ability to develop into specific 

 structures (Dalcq and Pasteels, 1938). 



PREFORMATIONISM - arrangement of parts of 

 the future embryo are spatially identical in 

 the egg (ovist) or in the homunculus of 

 sperm (spermist); anlagen of all parts of 

 the organism are already present in the 

 egg (or sperm). 



PREFUNCTIONAL PERIOD - period during 

 which the morphological and histological 

 differentiations proceed to prepare the or- 

 gans for functioning (Roux). 



PRESUMPTIVE - the expected (e. g. , the fate 

 of a part in question) based on previous 

 fate-map studies. 



PRIMORDIA, PRESUMPTIVE - place and extent 

 of prospective values of early gastrular sur- 

 face as regards its realization into specific 

 organ areas in the normal process of devel- 

 opment. Not necessarily checked by self- 

 differentiating technique. 



PRIMORDIUM - the beginning or earliest dis- 

 cernible indication of an organ. Syn. , rud- 

 iment, anlage. 



PRONUCLEUS - either of the gametic nuclei in 

 the egg after fertilization and before syn- 

 gamy; female pronucleus is the mature egg 

 nucleus after the elimination of the polar 

 bodies, distinct from the germinal vesicle 

 which is the pre-maturation nucleus. 



PROSPECTIVE SIGNIFICANCE - the normal 

 fate of any part of an embryo at the begin- 

 ning of development. Syn. , prospective 

 Bedeutung, Potentialite' reelle. 



PROTANDROUS - hermaphroditism in which the 

 male elements mature prior to the female. 



PROTHETELY - the appearance of structures 

 at an early stage of development which nor- 

 mally appear later (e.g. , pupal organs in 

 larval insects). Opposed to metathely. 

 (Schultze) 



PROTOGYNOUS - hermaphroditism in which the 

 female elements mature prior to the male. 



PROTOPLASMIC BRIDGE THEORY - (See 

 Hansen's theory and plasmadesmata. ) 



PYCNOSIS - increase in density of the nucleus 

 (or the cytoplasm) which may be hyper- 

 chromatic. Pycnotic cells in the central 

 nervous system are called chromophile 

 cells. Such cells have an increased affin- 

 ity for haematoxylin and methylene blue. 



PYGOPAGUS - rump union in conjoined twins. 



RACHISCHISIS - cleft spine, due to failure to 

 close completely. 



RANDZONE - term (German) for ma.rginal zone, 

 the line between the animal and the vegetal 

 hemispheres of amphibian eggs or the region 

 of initial involution for gastrulation. 



RATE-GENES - one and the same gene may lead 

 to different rates of formation of specific 

 materials such as melanin. 



REALISATORSYSTEM - pertaining to the non- 

 specific complexity of the metabolism-ap- 

 paratus which guarantees the normal course 

 of determination and topogenetic transfor- 

 mations in a blastema. (Lehmann. ) (See 

 determination. ) 



REALIZATION FACTOR - factor involved in the 

 achievement of a certain end organ produc- 

 tion, often associated with the establishment 

 of a gradient. 



RECONSTITUTION - an aspect of regeneration 

 where a new organ is formed within old tis- 

 sues rather than by regeneration from a cut 

 surface. A re-arrangement of parts to give 

 new form, particularly in hydroid experi- 

 ments (see blastema). 



RECOVERY, DIFFERENTIAL - differential ac- 

 climatization in a gradient system where a 

 low concentration of depressants indicates 

 that regions of highest activity show greatest 

 powers of adjustment. 



RECUPERATION - the reappearance of compe- 

 tence at a late stage in development (e. g. , 

 limb or tail blastema cells). 



REDIFFERENTIATION - secondary differentia- 

 tion within the area delimited by the term 

 modulation. (Kasahara, 1935: Arch. f. Exp. 

 Zell. 18). A return to a position of greater 

 specialization in actual and potential func- 

 tions (Bloom, 1937: Physiol. Rev. 17). 



REDUPLICATION - double or even treble 



growths (e. g. , limbs) connected with one 

 another at some point along their length, 

 reduplicated member being (usually) a mir- 

 ror image of the original (see Bateson's Rule). 



REGENERATION - repair or replacement of lost 

 part or parts by growth and differentiation 

 past the phase of primordial development. 

 The vast organizing potencies of the different 

 regions of the early embryo are lost after 

 the completion of development and there re- 

 main only certain regions of the body which 

 are said to be capable of regeneration. Re- 

 generative powers are more extensive among 

 embryos and adults of phyletically low forms. 



REGENERATION, BIAXIAL- regeneration which 

 leads to two apical or two basal regions, 

 accomplished in a form like Planaria by 

 cutting off the head and splitting the body 

 from the anterior cut surface, or from the 

 posterior. The latter procedure will often 

 give rise to a crotch head. 



REGENERATION, PHYSIOLOGICAL - changes 

 which occur as a part of the life cycle of the 

 organism. 



