U78 GLOSSARY 



STIMULATION, DIFFERENTIAL - varying responses of a gradient system to favorable conditions, as when an 

 optimally high ten^wrature is applied to a regenerating Planarlan and a bigger and better head re- 

 sults than under normal (temperature) conditions, (See inhibition, differential.) 



STIMULUS, FOIMATIVE - concentration of (chemical) substance In the dorsal lip of the blastopore leading 

 to the formation and demarcation of embiyonic fields. 



STIMULUS, OXYGENOTACTIC - differential stimulation of a developing organism by exposure to oxygen. Pre- 

 sumably a factor in the spreading of the blastoderm (chick) oyer the yolk. Syn., oxygenotaxi s . 



STOKE' S LAW - formula for determining viscosity V = ^'^^ ^g'n'^^ 



(formula generally omits c and q) where V is the speed at which granules travel through cytoplasm 

 under a centrifugal force of cq absolute units; g is the gravity constant; cT is the specific gravity 

 of the granules; p is the specific gravity of the cytoplasm; a is the radius if the granules; n is 

 the coefficient of viscosity of the cytoplasm; q is a factor which allows for the fact that there 

 are many granules plus the displacement of cytoplasm in granule movement. 



SUBSTRATE - the substance which is acted upon by an enzyme. 



SUCKER - adhesive, cementing organ of the oral region of anuran larvae. 



SUSCEPTIBILIIY, DIFFERENTIAL - evidence of non-homogeneity when diffusely applied injurious agent brings 

 about varying local reactions on the embryo. 



SYMPODIA - fusion, 'to varying degrees, of the legs (e.g., mermaid or siren condltlonl). 



SYNCYTIUM - propogation of nuclei with cytoplasmic growth but without cytoplasmic division so that there 

 results a mass of protoplasm with many and scattered nuclei but with inadequate cell boundaries 

 (e.g., chick marginal periblast and adult Nematodes). 



SYNDACTYLY - either bony fusion or fleshy webbing of the digits, generally the second and third digits 

 being Involved. Probably inherited in man. 



SYNERESIS - a segregation of the colloidal phases, a corollary of ageing. 



SYNGAMY - fusion of gametes, applied specifically to the merging of sperm and egg nuclei. 



SYNOPHTHALMIA - fusion of the eyes as in cyclopia. 



SYNTONIC FACTOR - some regulating force which enables a particular cell to live harmoniously with other 

 cells of the same type so that an organ will develop, not found in tissue cultures of cells Isolated 

 prior to differentiation, present during organogenesis. 



SYNTONY - Indwelling integration of parts ( Heidenhaln) ; a natural force within and between cells develop- 

 ing from the specific organization of living matter. 



TACBYAUXESIS - positive heterogony (Needham, igltO). 



TACHYGENESIS - speeding up and compression of ancestral stages in development. 



TACTILE DISPLACEMENTS - movements of parts of the embryo relative to each other, resulting in definite 

 formations and distributions of the germinal material; evidence of organizational influences. 



TELOBIOSIS - terminal fusion of embryos through operative procedures (see parabiosis). 



TENDENZEN - (German) autonomous abilities of a germ layer to reach developmental capacities as such 

 without the influence of inductive effects (Lehmann, Raven). (See neighborwise and selfwlse.) 



TERATOGENETIC - abnormality producing. 



TERATOLOGY - study of the causes of monster and abnormality formation. 



TERATOMA - structure which results from random differentiations; malignant assembly of tissues, often 



well differentiated histologically, generally embedded in an otherwise healthy organ. Some use term 

 embryoma to refer to histological differentiation and teratoma to mean both histological and mor- 

 phological differentiation of the abnormal growth. 



TETRAD - precocious splitting of the chromosomes in anticipation of both maturation divisions. 



THIXOTROPY - isothermal reversible sol-gel transformations (Fremdllch'a monograph). A thixotropic gel 

 will liquefy if shaken or stirred, later to return to its previous consistency. 



THORACO-GASTROSCHISIS - failure of the body wall to close along the mid-ventral line, including the 

 thoracic region. 



THORACOPAGUS - thoracic union of conjoined twins. 



TISSUE CULTURE - condition where an explant is able to survive and manifest vital activity; in vitro as 

 opposed to in vivo culturlng of excised tissues or organs (see isolation culture). 



TOGOGENESIS - all of the processes of novement which result in structure formation. 



TOTIPOTENCY - related to theory that the isolated blastomere is capable of producing a complete organism. 

 Roux (1912) Included several faculties such as (1) for self-differentiation; (2) for influencing dif- 

 ferentiation or induction of other parts; (5) for specific reaction to differentiating Influences as 

 in dependent differentiation. 



TRANSPLANT - an embryonic area (cell or tissue) removed to a different environment. Syn., graft. 



TBANSPLAOTATION - transfer of an embryonic blastema from one region to another of from one germinal layer 

 to another. Incorporation of an isolated fragment by a living organism, not merely the sticking on 

 of a graft. 



TRANSPLANT, AUTOPLASTIC - exchange of different parts within the same organism. 



TRANSPLANT, HETEROPLASTIC - exchange of parts between individuals of different species but within the 

 same genus (e.g., from Amblystoma punctatum to A. tigrinum) . 



TRANSPLANT, HETEROTOPIC - graft location different from graft source; exchange made to a non-ljomologous 

 region of the host; transplantation to a new site. 



TRANSPLANT, HOMOPLASTIC - grafts exchanged between members of the same species. Syn., homoloplaetlc 

 transplant. 



