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GLOSSARY 



TRANSPLANT, HOMOTOPIC - graft location 

 the same as the graft source; transplant to 

 the identical site or homologous region. 

 Syn. , orthotopic. 



TRANSPLANT, XENOPLASTIC - graft between 

 organisms of different genera or those still 

 further resolved phylogenetically. Graded 

 series would be autoplastic-heteroplastic - 

 xenoplastic. 



TRIASTER - abnormal mitotic figure possessing 

 three asters generally causing irregular 

 distribution of chromosomes and abnormal 

 cleavages. Other multiple aster conditions 

 moted, (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. 



TRITOGENY - one-third of a fragment (see 

 merogony). 



TROPHIC - the action of the nervous system in 

 the absence of which the muscle tonus fails 

 and in consequence, regeneration is im- 

 possible. 



TROPHOCHROMATIN - nutritive chromatin of 

 the nucleus. 



TRUE KNOT - slipping of the fetus through a 

 looped umbilical cord to produce a true 

 knot, distinguished from looped blood ves- 

 sels which cause external bulgings called 

 false knots. 



TWINS, IDENTICAL - true twins, from a single 

 egg and having common membranes and 

 umbilicus. 



TWINS, ORDINARY - pleural pregnancy result- 

 ing from the fertilization of separate ova 

 simultaneously liberated from individual 

 follicles. Separate development, implanta- 

 tion, decidua capsularism, and fetal mem- 

 branes. 



UMHULLUNG - (German) the process of wrap- 

 ping an inductor in sheets of competent ecto- 

 derm to test its inductive power. 



UNIPOTENT - attribute of certain cells which 

 can give rise to only one simple type of dif- 

 ferentiation; presumptive fate and presump- 

 tive potency are identical. 



VALUE, PROSPECTIVE - the realization value 

 of a part of the sum total represented by the 

 prospective potencies. 



VEGETATIVISATION - shifting of the presumptive 

 fate of normal ectoderm to become endoderm. 

 Syn. , vegetalization, endodermization. 

 Opposed to animalization. 



VERMIFORM CELL TYPE - elongated form of 

 isolated embryonic cells with finger-like 

 protuberances at the antipole of the coated 

 side (Holtfreter). 



VESICLE, GERMINAL - nucleus of the egg while 

 it is a distinct entity and before the elimina- 

 tion of either of the polar bodies. 



VISCOSITY - measure of inner molecular fric- 

 tion (see Stoke's Law). 



VITAL STAINING - localized staining of embry- 

 onic areas with vital, non-toxic dyes, for 

 purposes of studying morphogenetic move- 

 ments (method of Roux). 



VITALISM - a philosophical approach to biolog- 

 ical phenomena which bases its proof on the 

 present 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 supra-scientific or super-natural. 

 Effective guidance in development by some 

 non-material agency (see 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 de- 

 rived (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 mem- 

 brane. Syn. , zona radiata (mammals). 



WEBER' S-LAW - the degree of sensitivity to a 

 stimulus in any reacting system is not con- 

 stant 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 account 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 premaxilla be- 

 yond the surface of the face, accompanying 

 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 moUusce 

 embryo in which there is actually almost no 

 yolk, but it appears hernia-like from one of 

 the early blastomeres, disappearing between 

 cleavages and capable, when isolated, of giv- 

 ing rise to a dwarfed larva. Syn. , antipolar 

 or basal lobe. Opposed to polar lobe. 



YOLK NUCLEI - bodies responsible for preco- 

 cious digestion of yolk, derived from nucle- 

 oli which break up and pass out through the 

 nuclear membrane. Centers of yolk organiz- 

 ation during the growth period of oogenesis. 



