GLOSSARY 



489 



NUCLEAR MEDIUM - calcium free but other- 

 wise balanced and isotonic salt medium in 

 which the isolated germinal vesicle can 

 survive for some time. 



NUCLEOFUGAL - refers to outgrowth in two or 

 more directions from the nuclear region as 

 a center, such as in the formation of myelin 

 around a nerve fiber, starting at the sheath 

 cell nucleus as a center and growing in two 

 directions. 



NUSSBAUM'S LAW - the course of the nerve with- 

 in the muscle may be taken as the index of 

 the direction in which that particular mus- 

 cle has grown. 



OEDEMA - excessive accumulation of water 

 (lymph) in the tissues and cavities of the 

 body; may be subcutaneous and/or intra- 

 cellular. Due to a block in drainage chan- 

 nels and generally associated with cardiac 

 inefficiency. 



OMNIPOTENT - used in connection with a cell 

 which could, under various conditions, 

 assume every histological character known 

 to the species, or which, by division, could 

 give rise to such varied differentiations. 



ONTOGENY - developmental history of an or- 

 ganism; the sequence of stages in the early 

 development of an organism. 



"OMNE VIVUM E VIVO" - all life is derived 

 from pre-existing life (Pasteur). 



"OMNIS CELLULA E CELLULA" - all cells 

 come from pre-existing cells (Virchow). 



OOPLASM - cytoplasmic substances connected 

 with building rather than reserve materials 

 utilized in the developmental process. 



OPTICO-OCULAR APPARATUS - includes all 



the structures related to the eye: optic ves- 

 icles, optic stalks, and primary optic 

 chiasma, which develop from the simple 

 median anlage precociously found in the 

 medullary plate (LePlat, 1919). 



ORGAN-FORMING SUBSTANCE - substances 

 which, by chemo-differentiation and seg- 

 regation are localized in different blasto- 

 nneres bringing about a mosaic of develop- 

 ment. 



ORGAN, RUDIMENTARY - organ which is 



present but without any detectable physio- 

 logical manifestation. 



ORGANIC POINTS THEORY - discarded theory 

 of Bonnet and yet much like chemo-differ- 

 entiation. The preformed determinants are 

 unequally distributed between blastomeres 

 during early cleavage. 



ORGANICISM - laws of biological systems to 

 which the ingredient parts are processes 

 are subordinate; idea of organism as 

 whole (Loeb). 



ORGANIZATION - indicated by the inter -depen- 

 dence of parts and the whole. "When ele- 

 ments of a certain degree of complexity 



become organized into an entity belonging 

 to a higher level of organization" says Wad- 

 dington, "we must suppose that the coher- 

 ence of the higher level depends on proper- 

 ties which the isolated elements indeed pos- 

 sessed but which could not be exhibited until 

 the elements entered into certain relations 

 with one another. " Relations beyond mere 

 chemical equations; bordering on the philo- 

 sophical idea. Process of differentiation 

 or specialization which takes place accord- 

 ing to a definite pattern in space and time, 

 not chaotically in the direction of haphazard 

 distribution (see Gestalten). 



ORGANIZER - the chorda-mesodermal field of 

 the amphibian embryo; a living tissue area 

 which has the power of organizing indifferent 

 tissue into a neural axis. Organizer is 

 more than an evocator or inductor because 

 definite axial structures are caused to de- 

 velop. Term first used by Spemann to des- 

 cribe a "dorsal quality" qualitatively differ- 

 ent from vegetal hemisphere material. 

 Term organizer now used for graded induc- 

 tions such as primary or first grade organ- 

 izer (dorsal lip; induces neural axis) sec- 

 ondary or second grade organizer (optic cup 

 induces lens); and tertiary or third grade 

 (annulus tympanicus induced tympanic nnem- 

 brane formation). 



ORGANIZER, NUCLEOLAR - localized region 

 of a particular set of chromosomes where 

 the nucleolus is found, each nucleolus being 

 associated with a set of chromosomes. 



ORGANOGENESIS - emancipation of parts from 

 the whole; appearance or origin of morpho- 

 logical differentiation. 



ORTHOTOPIC - transplant to homologous region. 



OSMOTIC PRESSURE - P equals kCT; P is the 

 force under which water tends to pass 

 through a membrane into a substance that 

 cannot diffuse through this same membrane 

 (e. g. , sugar and collodion membrane) and 

 this force is directly proportional (k) to the 

 molecular concentration (C) of the substance 

 (sugar) and to the absolute temperature (T). 

 The terms isotonic, hypertonic, and hypo- 

 tonic are used to express osmotic pressure 

 relations such as exist between the cell con- 

 tents and its environment. 



OTOCEPHALY - tendency to fusion or approx- 

 imation of ears, accompanying cyclopia. 



OUTGROWTH NEURONE THEORY - the cells 

 found along the course of a nerve fiber, the 

 fiber developing as a protoplasmic out- 

 growth (extension) from a single ganglion 

 cell. 



OVOPHILE - presumed receptor portion of am- 

 boceptor suitable to receive the egg recep- 

 tor, anti-fertilizin, or blood inhibitors, in 

 the fertilizin reaction (Lillie). 



OVIPOSITION - the process of egg laying. 



