1»72 GLOSSARY 



MOBPHOGENESIS - all of the topogenetlc processes which result In structure formation; the origin of char- 

 acteristic structure (form) In an organ or In an organism compounded of organs. 



MORPHOGENETIC MOVEMEMTS - cell or cell area movements concerned with the formation of germ layer (e.g., 

 during gaatrulatlon) or of organ prlmordia. Syn., G«staltungsbewegungen. 



MOHPHOGENETIC POTENTIAL - product of a reaction between the cortex and the yolk Just sufficient to bring 

 about response in a competent area; threshold value (Dalcq and Pasteels). 



MORPHALLAXIS - an old part transformed directly into a new part or whole organism, a type of regeneration, 

 resulting in a whole from a part (e.g., each piece of a dissected Planarla or Tubifex becomes a com- 

 plete organism) . 



MOSAIC - a type of egg or development In which the fate of all parts are fixed at an early stage, possibly 

 even at the time of fertilization. Local Injury or excisions generally result In the loss of specific 

 oiigans in the developing embryo. Such eggs or embryos react by recovery to such experimental proce- 

 dures as blastomere separation, parabiosis or merogony. Opposed to regulative development. 



MOVEMEOT, FOBMATIVE - localized changes in cell areas resulting in the formation of specifically recogniz- 

 able embryonic regions (Vogt). 



MOVmEOT, HCMOLOGOUS - movement of homologous muscles in transplanted limbs, the synchronous contraction 

 of muscles. 



NACHBAHSCHAFT - morphogenetlc effects produced by contact with other tissues or structures of a develop- 

 ing organ; contiguity effects. 



NECBOHOHMONES - the chemical substances produced by degenerating nuclei which cause the premature and 

 incomplete divisions of oocytes in sexually mature mammals and in the formation of oligopyrene 

 spermatozoa in Mollusca. 



NECBOSIS - local death of a cell or group of cells, not the whole body. 



NEIGHBOBWISE - the reaction of a transplant appropriate to its new environment, indicating its plas- 

 ticity, pluri potency, or lack of determination. Syn., Artsgemass. 



NEMAMEEE - one of the physical units composing a gene-string or genonema, which carries the genes. May 

 be composed of several genes, or a single gene may extend over several nemameres. Governs bio- 

 physical reactions of the gene-string. 



NECMOBPHOSIS - new part not only different from part removed but also like an organ belonging to another 

 part of the body; or unlike any organ of the body. 



NEOPLASM - a new growth, generally a tumor. Histologically and structurally an atypical new formation. 



NEOTONY - sexual maturity in the larval stage; a condition of many urodeles (e.g., Necturus, Azolotl) 

 and of experimentally produced thyroidless anuran embryos where the larval period Is extended or 

 retained, i.e., the larvae fall to go through metamorphosis. Appearance of larval conditions In 

 the adult. 



NEURAL CREST - a continuous cord of ectodermally derived cells lying on each side in the angle between 

 the neural tube and the body ectoderm, separated from the ectoderm at the time of closure of the 

 neural tube and extending from the extreme anterior to the posterior end of the embryo; material 

 out of which the spinal and possibly some of the cranial ganglia develop, and related to the develop- 

 ment of the sympathetic ganglia and parts of the adrenal gland by cell migration. 



rffiUBOBIOTAXIS - concentration of nervous tissue takes place in the region of greatest stimulation. 



NEUEOGEN - an evocator which causes neural Induction In vertebrates. May include the organizer, chemical 

 substances, carcinogens, oestrogens, etc. 



NEUBOGENESIS, MECHANICAL HYPOTHESIS OF - mechanical tension of plasma medium in any definite direction 

 is said to orient and aggregate the fibrin micellae in a corresponding direction. 



NEUROHUMOBS - hormone-like chemical substance produced by neroua tissue, particularly the ends of develop- 

 ing nerves which consequently act as stimulating agents. 



NEURULA - stage in embryonic development which follows gaatrulatlon and during which the neural axis is 



forned and histogenesis proceeds rapidly. The notochord and neural plate are already differentiated, 

 and the basic vertebrate pattern is indicated. 



NEUTRAL MEDIUM - an environmental medium for the embryo which is free from any chemical or physical in- 

 ductors, and is physiologically isotonic. 



NORMALIZING - formative action anchored in the organization associated with the determination of develop- 

 ment, not super-material entelechy but an Integral part of the organism Itself. Integrating and 

 balancing tendencies. 



mjCLEAL REACTION - sections of tissue hydrolyzed with HCl before treating with Schlff's reagent may give 

 a characteristic red or purple color known as the nucleal reaction. (See Feulgen reaction.) 



NUCLEAR MEDIUM - calcium free but otherwise balanced and isotonic salt medium in which the Isolated germinal 

 vesicle can survive for some time. 



NUCLEOFUGAL - refers to outgrowth In two or nore directions from the nuclear region as a center, such as in 

 the formation of nyelln 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 within the muscle may be taken as the Index of the direction in 

 which that particular muscle has grown. 



OEDBMA - excessive accumulation of water (lymph) in the tissues and cavities of the body; niay be sub- 

 cutaneous and/or intracellular. Due to a block in drainage channels and generally associated with 

 cardiac Inefficiency. 



