GLOSSARY U79 



TEANSPLANT, HOMOTOPIC - graft location the same aa the graft source; transplant to the identical site or 



homologous region. Syn., orthotopic. 

 TRANSPLANT, XENOPLASTIC - graft between organiama of different genera or those still further resolved 



phylogenetically. Graded series would be autoplastic-heteroplastic - xenoplastic. 

 TBIASTER - abnormal mitotic figure possessing three asters generally cauaing irregular distribution of 



chromosomes and abnormal cleavages. Other multiple aster conditions noted, (e.g., tetraster, etc.). 

 TRIGGER REACTION - condition where the character, pattern, vigor, progress and speed of a response are in 



no way related to the releasing event. 

 TBITOGENY - one-third of a. fragment (see merogony) . 



TROPHIC - the action of the nervous system in the absence of which the muscle tonus faila and in conse- 

 quence, regeneration is impossible. 

 TEOPHOCEBOMATIN - nutritive chromatin of the nucleus. 

 THUE KNOT - slipping of the fetus through a looped umbilical cord to produce a true knot, distinguished 



from looped blood vessels which cause external bulgings called false knots. 

 TWINS, IDEHTICAL - true twina, from a single egg and having common membranes and umbilicus. 

 TWINS, ORDINARY - pleural pregnancy resulting from the fertilization of separate ova simultaneously 



liberated from individual follicles. Separate development, implantation, decidua capaularism, and 



fetal membranes . 



UMHULLUNG - (German) the proceas of wrapping an inductor in sheets of con5)etent ectoderm to teat its in- 

 ductive power. 



UNIPOTENT - attribute of certain cells which can give rise to only one simple type of differentiation; 

 presumptive fate and presumptive potency are identical. 



VALUE, PROSPECTIVE - the realization value of a part of the aum total represented by the proapective 

 potencies. 



VEGETATIVISATION - shifting of the presuii5)tlve fate of normal ectoderm to become endoderm. Syn., vegeta- 

 lization, endoderminzatlon. Opposed to animallzatlon. 



VERMIFORM CELL TYPE - elongated form of Isolated embryonic cells with flnger-llke protuberances at the 

 antipole of the coated side ( Holtfreter) . 



VESICLE, GERMINAL - nucleus of the egg while it is a distinct entity and before the elimination of either 

 of the polar bodies. 



VISCOSITY - measur'e of inner molecular frlctfon (see Stoke 'a Law). 



VITAL STAINIMJ - localized staining of embryonic areas with vital, non-toxic dyes, for ptirpoaes of study- 

 ing morphogenetlc movementa (method of Eoux). 



VITALISM - a philosophical approach to biological phenomena which bases its proof on the proaent inability 

 of scientists to explain all the phenomena of development. Idea that biological activities are 

 directed by forces neither physical nor chemical, but which must be eupra-sclentlflc or super-natural. 

 Effective guidance in development by some non-material agency ( aee mechanism). 



VITELLIN - egg-yolk phospho-protein. 



VITELLINE - adj., pertains to yolk, vein, or membrane. 



VITELLINE MEMBRANE - delicate, outer, non-living and non-cellular egg membrane derived (while In the ovary) 

 probably by the Joint action of the egg and its follicle cells. It is probably the same membrane that 

 is lifted off of the egg at fertilization and is subsequently known as the fertilization membrane. 

 Syn., zona radiata (mammals). 



WEEEE'S-LAW - the degree of sensitivity to a stimulus in any reacting system is not constant but depends, 

 not alone on the nature of the stimulus, but upon the period of life and the strength of an already 

 existing stimulus. A stimulus therefore represents a change, but a reacting system takes Into ac- 

 count any pre-existing stimulus upon which this change is built. Theory that equal relative differ- 

 ences between stimuli of the same kind are equally perceptible. 



WOLF SNOUT - projecting of the premaxllla beyond the surface of the face, accoii5>einylng double (hare) lip 

 and sometimes a cleft palate. 



XANTHOLEUCOPHORES - crystals and soluble yellow pigment; cells bearing such. 

 XANTHOPHORES - yellow pigment in solution; cells bearing this yellow pigment. 

 XIPHOPAGUS - xiphoid fusion of conjoined twins; sometimes the skin alone. 



YOLK LOBE - lobe of early developing mojluace embryo in which there la actually almost no yolk, but it 

 appears hemla-llke from one of the early blastomeres, diaappearing between cleavages and capable, 

 when Isolated, of giving rise to a dwarfed larva. Syn., antipolar or basal lobe. Opposed to polar 

 lobe. 



YOLK NUCLEI - bodies responsible for precocious digestion of yolk, derived from nucleoli which break up 

 and pass out through the nuclear membrane. Centers of yolk organization during the growth period 

 of oogenesis. 



