484 



GLOSSARY 



INDUCliON, DiRECr - case where a chemical 

 compound acts in a manner similar to the 

 naturally occurring inductor to produce a 

 new neural axis in competent ventral ecto- 

 derm. 

 INDUCTION, HETEROGENETIC - when an or- 

 ganizer induces something other than itself, 

 such as secondary organizer optic vesicle 

 inducing lens formation. 

 INDUCTION, HOMOIOGENETIC - where em- 

 bryonic part induces its like (e. g. , medul- 

 lary plate induces medullary plate). 

 INDUCTION, INDIRECT - induction by a chem- 

 ical 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 in- 

 ductor. 

 INDUCTOR - a loose word which includes both 

 organizer and evocator (Needham). Gener- 

 ally means a piece of living tissue which 

 brings about differentiations within other- 

 wise indifferent tissue. 

 INDUCTOR, NUCLEAR - a morphogenetic stim- 

 ulating substance which is derived from the 

 nucleus and therefore bears hereditary in- 

 fluences, but generally operating within the 

 cell in question. The influence may be dif- 

 fusible. 

 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. , Weckung. 

 INFUNDIBULUM - funnel-like evagination of 

 the floor of the diencephalon which, along 

 with the hypophysis, will give rise to the 

 pituitary gland of the adult. 

 INGRESSION - inward movement of the yolk en- 

 doderm of the amphibian blastula. (Nicholas, 

 1945.) 

 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 

 deternnined neuromuscular structure when 

 adequate internal and external stimuli act 

 upon it. " (Hartmann, 1942, Psychosomatic 

 Med. 4:206.) 

 INSTITUTION - labile determination or compe- 

 tence of early germ (Graeper). 

 INTERSEX - an individual without typical sexual 

 differentiation. Not hermaphrodite. 



INVAGINATION - movement by in- sinking 



(Einstulpung of Vogt) of the egg surface and 

 forward migration (Vordringen) involving 

 displacement of inner materials. The fold- 

 ing or inpushing of a layer of (vegetal hem- 

 isphere) cells into a preformed cavity (blas- 

 tocoel) as one of the methods of gastrulation. 

 Not to be confused with involution. 



INVOLUTION - rotation of a sheet of cells upon 

 itself; movement directed toward the inte- 

 rior of an egg; the rolling inward or turning 

 in of cells over a rim. One of the move- 

 ments of gastrulation (e. g. , chick). Syn. 

 embolic invagination (Jordan); einroUung, 

 or umschlag (Vogt). 



IRIDIOCYTES - inorganic salt crystals. 



ISAUXESIS - relative growth comparisons in 

 which the rate of the part is the same as 

 that of the whole. (Syn. , isogony. ) (Need- 

 ham, 1940.) 



ISO-AGGLUTININ - (Syn. , for fertilizin. ) 



ISO-ELECTRIC POINT - set of conditions un- 

 der which the protein tends to give off hy- 

 drogen ions just sufficient to balance the 

 tendency to give off hydroxyl ions; a state 

 where the ionization of the protein is bal- 

 anced. 



ISOGONY - proportionate growth of parts so 

 that growth coefficient is unity and there 

 are constant relative size differences. 

 Equivalent relative growth rate. 



ISOLATION - removal of a part of a developing 

 organism and its maintenance in the living 

 condition as in tissue cultures. Physiolog- 

 ical isolation may be achieved by interpos- 

 ing a mass of inert material (e. g. , yolk) 

 between two regions. The bifurcations of 

 regenerating limbs or the production of 

 double hearts by interposing an inert bar- 

 rier or one which is not subject to assim- 

 ilative induction. 



ISOMETRY - study of relative sizes of parts of 

 animals of the same age. 



ISOTROPIC - synonym for pluripotent (Lillie, 

 1929). 



ISOTROPY - originally used (Pfluger, 1883) to 

 mean absence of predetermined axes within 

 the egg; now means condition of egg where 

 any part can give rise to any part of the 

 embryo (i. e. , equivalence of all parts of 

 the egg protoplasm). 



JANICEPS - Janus monster, face to face union 

 of conjoined twins. 



JANUS EMBRYO - double monster with faces 

 turned in opposite directions. Syn. , dup- 

 licitas cruciata typica. 



JELLY -mucin covering of (amphibian) egg, de- 

 rived from the oviduct and applied to the out- 

 side of the vitelline membrane. In Frog, ap- 

 parently necessary for successful fertilization. 



