1*68 GLOSSARY 



HYPOPLASIA - undergrowth or deficiency In the elements composing a part. 



ffifPOTHESIS - a complemental supposition; a presumption based on fragmentary but suggestive data offered to 

 bridge a gap in incomplete knowledge of the facte. May even be offered as an explanation of facts un- 

 proven, to be used as a basis of expectations to be subject to verification or disproof. 



EfPOTHESIS, WORKING - an attempt to find an answer to sone feature of a conjilete biological situation by 

 utilizing accepted physical and chemical principles. 



BJfSTEBOTELy - formation of a structure is relatively delayed. 



IDIOPLASM - equivalent to germ plasm of Welsmann. Dissimilar determinant imits of self-differentiating 

 capacity (genes) each representing some part or character of the orgeinism arranged in some plan 

 comparable to the future arrangement of organic parts (Welsmann). 



IMPLANT - tissue or organ removed to an abnormal position; graft. 



IMPLANTATION - process of adding, superimposing, or placing a graft (or a chemical fraction thereof) with- 

 in a host without removal of anything from the host. Implants may be into the body cavity or into 

 the orbital or anterior eye chamber cavities. 



INCOMPATIBILITY - opposed to affinity; tendency of cells or cell groups to repel each other when removed 

 from their normal environmsnt. May be expressed in terms of cytolysis or histolysis of one of the 

 cells or groups of cells. 



INDIVIDUATION - assimilative induction concerned with regional character of the structure derived in 

 response to (living) organizer activity; opposed to evocational responses. Refers to process in 

 different regions as affected by the organizer, not by a single chemical substance such as an 

 evocator. Regional nature affected by host environment. 



INIUCTION - causing cells to form an embryonic structure which neither the Inductor nor the reacting cells 

 would form if not combined; the calling forth of a morphogenetic functional state in a competent 

 blastema as a result of contact. In contrast with evocation. Induction is successive, and purposeful 

 In the sense that one structure leads to another. Sometimes loosely used to Include evocator influ- 

 ences from non-living materials. Originally meant diversion of development from epidermis toward 

 medullary plate (Marx, 1925). 



INDUCTION, ASSIMILATIVE - transformation of one presumptive area into a different direction under the 

 influence of inductive forces (Spemann). 



INDUCTION, AUTONOMOUS - if the inducing Implant and the host do not cooperate to form an harmonious whole, 

 the material of the Implant may not be used although the inductive forces are uninjialred. The in- 

 ductor takes no part in the inducted structure (e.g., all chemical inductions). Opposed to comple- 

 mentary Induction. 



INDUCTION CAPACITY - organizational capacity; acquired with age and subsequently lost. 



INDUCTION, COMPLEMENTARY - when the inductor, using some of its own material, cotqiletee Itself out of the 

 reacting system (host material); (e.g., when presumptive epidermis is transplanted to presumptive 

 brain region and the embryo completes itself out of the transplanted material). Opposed to 

 autonomous induction. 



INDUCTION, DIRECT - case where a chemical compound acts in a manner similar to the naturally occurring 

 inductor to produce a new neural axis in competent ventral ectoderm. 



INDUCTION, HETEROGENBTIC - when an organizer induces something other than Itself, such as secondary 

 organizer optic vesicle inducing lens formation. 



INDUCTION, HOMOIOGENBIIC - where embryonic part induces its like (e.g., medullary plate induces medullary 

 plate) . 



INDUCTION, INDIRECT - Induction by a chemical compound in ventral ectoderm of a new neural axis by the 

 liberation of a masked evocator in the reacting tissue. 



INDUCTION, PALISADE - induction of neural-like tissue but without tube formation; cells arranged in 

 palisade manner around an inductor. 



INDUCTOR - a loose word which Includes both organizer and evocator (Needham). Generally means a piece 

 of living tissue which brings about differentiations within otherwise indifferent tissue. 



INDUCTOR, NUCLEAR - a ncrphogenetic stimulating substance which is derived from the nucleus and there- 

 fore bears hereditary Influences, but generally operating within the cell in question. The influ- 

 ence may be diffusible. 



INFECTION - the acquisition of inductive power by a group of cells not normally possessing such power, 

 but acquiring it by diffusion from temporarily contiguous organizer material. Syn., Wecfcung. 



INFUNDIBULUM - funnel-like evaginatlon of the floor of the diencephalon which, along with the hypophysis, 

 will give rise to the pituitary gland of the adult. 



INGRESSION - inward movenent of the yolk endoderm of the amphibian blastula. (Nicholas, 19'*5. ) 



INHIBITION - restraint or nullification of a tendency to differentiate. 



INHIBITION, DIFFERENTIAL - restraint in a gradient field where toxic agents inhibit regeneration in the 

 most active regions. 



INHIBITION, TROPHIC - functional inhibition, contrasted with morphogenetic. 



INSTINCT - "the overt behavior of the organism as a whole" "which is in physiological condition to 



act according to its genetically determined neuromuscular structure when adequate internal and ex- 

 ternal stimuli act upon it." ( Hartmann, 19'*2, Psychosomatic Med. U:206.) 



INSTITUTION - labile determination or competence of early germ (Graeper). 



INTERSEX - an individual without typical sexual differentiation. Not hermaphrodite. 



INVAGINATION - movement by in-sinking (Elnstulpung of Vogt) of the egg surface and forward migration 

 (Vordringen) involving displacement of inner materials. The folding or Inpushing of a layer of 

 (vegetal hemisphere) cells into a preformed cavity (blastocoel) as one of the methods of gaatrula- 

 tlon. Not to be confused with involution. 



