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GLOSSARY 



MONSTER, ISCHIOPAGUS - double embryos, 



widely separated except at the tail; produced 

 by any means. 



MORPHOGENESIS - all of the topogenetic proc- 

 esses which result in structure formation; 

 the origin of characteristic structure (form) 

 in an organ or in an organism compounded 

 of organs. 



MORPHOGENETIC MOVEMENTS - cell or cell 

 area movements concerned with the forma- 

 tion of germ layer (e. g. , during gastrula- 

 tion) or of organ primordia. Syn. , Gestal- 

 tungsbewegungen. 



MORPHOGENETIC 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 

 Planaria or Tubifex becomes a complete 

 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 fertiliza- 

 tion. Local injury or excisions generally 

 result in the loss of specific organs in the 

 developing embryo. Such eggs or embryos 

 react by_recovery to such experimental 

 procedures as blastomere separation, para- 

 biosis or merogony. Opposed to regulative 

 development. 



MOVEMENT, FORMATIVE - localized changes 

 in cell areas resulting in the formation of 

 specifically recognizable embryonic regions 

 (Vogt). 



MOVEMENT, HOMOLOGOUS - movement of 



homologous muscles in transplanted limbs, 

 the synchronous contraction of muscles. 



NACHBARSCHAFT - morphogenetic effects pro- 

 duced by contact with other tissues or struc- 

 tures of a developing organ; contiguity 

 effects. 



NECROHORMONES - the chemical substances 

 produced by degenerating nuclei which 

 cause the premature and inconnplete divi- 

 sions of oocytes in sexually mature mam- 

 mals and in the formation of oligopyrene 

 spermatozoa in MoUusca. 



NECROSIS - local death of a cell or group of 

 cells, not the whole body. 



NEIGHBORWISE - the reaction of a transplant 

 appropriate to its new environment, indi- 

 cating its plasticity, pluripotency , or lack 

 of deternnination. Syn., Artsgemass. 



NEMAMERE - one of the physical units compos- 

 ing a gene-string or genonema, which car- 

 ries the genes. May be composed of several 

 genes, or a single gene may extend over 

 several nemameres. Governs biophysical 

 reactions of the gene-string. 



NEOMORPHOSIS - new part not only different 

 from part removed but also like an organ 

 belonging to another part of the body; or un- 

 like 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 thy- 

 roidless anuran embryos where the larval 

 period is extended or retained, i. e. , the 

 larvae fail to go through metamorphosis. 

 Appearance of larval conditions in the adult. 



NEURAL CREST - a continuous cord of ecto- 



dermally 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 

 extendingfrom 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 

 development of the sympathetic ganglia and 

 parts of the adrenal gland by cell migration. 



NEUROBIOTAXIS - concentration of nervous 



tissue takes place in the region of greatest 

 stimulation. 



NEUROGEN - an evocator which causes neural 

 induction in vertebrates. May include the 

 organizer, chennical substances, carcino- 

 gens, oestrogens, etc. 



NEUROGENESIS, MECHANICAL HYPOTHESIS 

 OF - mechanical tension of plasma medium 

 in any definite direction is said to orient and 

 aggregate the fibrin micellae in a correspond- 

 ing direction. 



NEUROHUMORS - hormone-like chemical sub- 

 stance produced by nerous tissue, particu- 

 larly the ends of developing nerves which 

 consequently act as stimulating agents. 



NEURULA - stage in embryonic development 



which follows gastrulation and during which 

 the neural axis is formed 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 chem- 

 ical or physical inductors, and is physiolog- 

 ically isotonic. 



NORMALIZING - formative action anchored in the 

 organization associated with the determina- 

 tion of development, not super-material 

 entelechy but an integral part of the organ- 

 ism itself. Integrating and balancing ten- 

 dencies. 



NUCLEAL REACTION - sections of tissue hy- 

 drolyzed with HCl before treating with 

 Schiff's reagent may give a characteristic 

 red or purple color known as the nucleal 

 reaction. (See Feulgen reaction. ) 



