GLOSSARY U73 



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. 



ONTOGETTf - developmental history of an organism; 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 CELLUTJl 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-OCULAE APPARATUS - includes all the structures related to the eye: optic vesicles, optic stalks, 

 and primaiy optic chiasma, which develop from the simple median anlage precociously found in the 

 medullary plate (LePlat, I919). 



OEGAN-FOBMING SUBSTANCE - substances which, by chemo-differentiatlon and segregation are localized in 

 different blastomeres bringing about a mosaic of development. 



OEGAN, HUDIMENTABY - organ which is present but without any detectable physiological manifestation. 



OBGANIC POINTS THEORY - discarded theory of Bonnet and yet much like chemo-differentiation. The preformed 

 determinants are xuiequally distributed between blastomeres during early cleavage. 



OBGANICISM - laws of biological systems to which the ingredient parts are processes are subordinate; idea 

 of organism as a whole (Loeb). 



OEGAMIZATION - indicated by the inter- dependence of parts and the whole. "When elements of a certain 

 degree of complexity become organized into an entity belonging to a higher level of organization" 

 says Waddlngton, "we must suppose that the coherence of the higher level depends on properties 

 which the isolated elements Indeed possessed but which could not be exhibited until the elements 

 entered into certain relations with one another." Relations beyond mere chemical equations; border- 

 ing on the philosophical idea. Process of differentiation or specialization which takes place 

 according to a definite pattern in space and time, not chaotically in the direction of haphazard 

 distribution (see Gestalten). 



OEGAHIZEE - 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 in- 

 ductor because definite axial structures are caused to develop. Term first used by Spemann to 

 describe a "dorsal quality" qualitatively different from vegetal hemisphere material. Term organizer 

 now used for graded inductions such as primary or first grade organizer (dorsal lip; Induces neural 

 axis) secondary or second grade organizer (optic cup induces lens); and tertiary or third grade 

 (tinnulus tympanicua Induced tympanic membrane formation). 



OEGAHIZEE, NUCLEOLAE - localized region of a particular set of chromosomes where the nucleolus is found, 

 each nucleolus being associated with a set of chromosomes. 



OEGANOGENESIS - emancipation of parts from the whole; appearance or origin of morphological differentia- 

 tion. 



OETHOTOPIC - transplant to homologous region. 



OSMOTIC PEESSUEE - 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 hypotonic are used to 

 express osmotic pressure relations such as exist between the cell contents and Its environment. 



OTOCEPHALY - tendency to fusion or approximation of ears, accompanying cyclopia. 



OUTGEOWTH NEUEONE THEOEY - the cells found along the course of a nerve fiber, the fiber developing as a 

 protoplasmic outgrowth (extension) from a single ganglion cell. 



OVOPHILE - presumed receptor portion of amboceptor suitable to receive the egg receptor, antl-fertlllzin, 

 or blood inhibitors. In the fertilizln reaction (Lillie). 



OVOPOSITIOM - the process of egg laying. 



OVOVrVIPAEITY' - condition in which egg contains enough yolk to carry the embryo to hatching. After this 

 stage the larva is liberated from the maternal organism without receiving further nourishment. 



OVULATION - the release of eggs from the ovaiy, not necessarily from the body. 



PAEDOGENESIS - relative retardation of the development of body structures as compared with the reproduc- 

 tive organs; reproduction during lar'^al stage; precocious sex development. 



PAEDCMOEPHOSIS - introduction of youthful characters Into the line of adults. 



PALINGENBIIC - term used for repeated or recapitulated stages which reflect the history of the race 

 (Haeckel). 



PARABIOSIS - lateral fusion of embryos by injuring their mirror surfaces and approximating them so that 

 they grow together (see teloblosis). 



PAETHENOGENESIS - development of the egg without benefit of spermatozoa; development stimulated by arti- 

 ficial means. 



PARTHENOGENESIS, ARTIFICIAL - activation of an egg by chemical or physical means (e.g., butyric acid, 

 hypertonic solutions, irradiation, needle prick, etc.) 



PAETHENOGENESIS, FACULTATIVE - eggs normally fertilized before development may, on occasion, develop when 

 fertilization is delayed before sperm penetration. 



PAETHENOGENESIS, NATURAL - maturation of the egg leads to development without the aid of spermatozoa 

 (e.g., some insects). 



PARTITION- COEFFICIENT - the factor which determines the size of any part at any time by parcelling out 

 materials; relative capacity for various parts of the embryo to absorb food from a common supply at 

 different times. Such coefficients are expressions of intrinsic growth potentials, so balanced In 

 normal development that no single structure can monopolize the nutriment to the detriment of other 

 structures. 



