GLOSSARY 1*75 



POLE, ANIMAL - the protoplasmic portion of a telolecithal egg from which the polar bodies are given off, in 

 «hlch the germinal vesicle is found, and which has the highest metabolism and gives rise to the princi- 

 pal parts of the nervous system and sense organs. Eegion of least yolk concentration. Syn., apical 

 pole or hemisphere (See anlmalization) . 



POLE, VEGETAL - region of the egg opposite the animal pole; region of lowest metabolic rate; pole with 

 greatest density of yolk in telolecithal eggs, generally the endoderm forming portion of the early 

 egg. (See vegetativisation. ) 



POLYDACTYLY - extra digits in hands or feet; in man probably inherited. 



POLYMBRYONY - natural isolation of blastomeres leading to the production of multiple embryos; develop- 

 ment of several embryos from a single zygote. 



POLYHYDRAMNIOS - condition where the amniotic fluid exceeds two liters. 



POLYPLOID - possessing a multiple number of chromosomes, such as triploid (3 times the haplold number) 

 tetraploid (k times the haploid), etc. Always more than the normal diploid number of the typical 

 zygote. (Winkler, 19 l6.) 



POLYPLOIDOGEN - a chemical substance which brings about the polyploid condition, usually by inhibiting 

 certain phases of nuclear division. 



POLYSPERMY - entrance into the egg of more than a single sperm, normally (e.g., chick and urodele) or 

 under pathological conditions (e.g., Anura, Echinodermata, Mollusca, etc.) (Hertwig, 1887; Boveri, 

 1907; Herlant, I9II). Normal polyspemy is sometimes called "physiological polyspemy" while the 

 abnormal is pathological, brought about by chemical or physical conditions (see Clark, I936. Bio. 

 Bull.). 



POST-GENERATION - regeneration out of newly formed rather than already differentiated tissues; restora- 

 tion of parts of the embryo by utilization of materials (unused) from an injured (cauterized) blas- 

 tomere (Eoux). 



POTENCY - ability to develop embryologically; capacity for completing destiny; ability to perform an 

 action; "future development verbally transformed to an earlier stage (Waddlngton) . The test of 

 potency is actual realization in development. It is not the same as competence. It is an explana- 

 tory rather than a descriptive term (Boux, I892) for developmental possibility." "A piece of an 

 embryo has the possibility of a certain fate before detennination, and the power to pursue* it 

 afterwards." (Needham, 191+2.) 



POTENCY, ACTIVE - cases of self-differentiation lAere potencies are realized in isolation even without 

 inductive forces (Bautzmann, 1929)- 



POTENCY, PASSIVE - potencies formed in the presence of Inductive forces only (Bautzmann, 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 coiqietence. 



POTENTIAL, MORPHOGENETIC - the strong or weak ability to develop into specific structures (Dalcq and 

 Pasteels, I958). 



PEEFOEMATIONISM - 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). 



PEERTNCTIONAL PERIOD - period during which the morphological and histological differentiations proceed 

 to prepare the organs for functioning (Eoux). 



PRESUMPTIVE - the expected (e.g., the fate of a part in question) based on previous fate-map studies. 



PRIMOBDIA, PRESUMPTIVE - place and extent of prospective values of early gastrular surface as regards 

 its realization into specific organ areas in the normal process of development. Not necessarily 

 checked by self-differentiating technique. 



PRIMORDIUM - the beginning or earliest discernible indication of an organ. Syn., rudiment, anlage. 



PRONUCLEUS - either of the gametic nuclei in the egg after fertilization and before syngamy; female 



pronucleus is the mature egg nucleus after the elimination of the polar bodies, distinct from the 

 germinal vesicle which is the pre-maturatlon nucleus. 



PROSPECTIVE SIGNIFICANCE - the normal fate of any part of an embryo at the beginning of development. 

 Syn., prospective Bedeutung, Potentlalite 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 normally appear later 

 (e.g., pupal organs in larval insects). Opposed to metathely. (Schultze) 



PBOTOGYNOUS - hermaphroditism in which the female elements mature prior to the male. 



PROTOPLASMIC BRIDGE THEORY - (See Hensen's theory and plasmadesmata. ) 



PYCNOSIS - increase in density of the nucleus (or the cytoplasm) which may be hyperchromatlc. I>ycnotlc 

 cells in the central nervous system are called chromophile cells. Such cells have an Increased 

 affinity for haematoxylin and methylene blue. 



PYGOPAOUS - rump union in conjoined twins. 



RACHISCHISIS - cleft spine, due to failure to close completely. 



RANDZONE - term (German) for marginal zone, the line between the animal and the vegetal hemispheres of 



amphibian eggs or the region of initial involution for gaetrulatlon. 

 RATE-GENES - one and the same gene may lead to different rates of formation of specific materials such 



as melanin. 



