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GLOSSARY 



MAUTHER'S FIBERS - two highly dillerentiated, 

 giant neurones found in the medulla of tele- 

 ost fishes and amphibia and possessing ex- 

 tensive dendritic connections; axones extend 

 from VIII cranial ganglion through the spinal 

 cord. The fibers are functional particularly 

 in maintaining the sense of equilibrium and 

 are indispensible for sustained rhythmic 

 motor reflexes. 

 MECHANICS, DEVELOPMENTAL - "analysis of 

 the first found results of the experimental 

 study of development of the egg. " (Morgan) 

 MECHANISM - assumption that biological proc- 

 esses do not violate physical and chemical 

 laws but that they are more than the mere 

 functioning of a machine because material 

 taken into the organism becomes an integral 

 part of the organism, through chemical 

 changes. Syn. , the scientific attitude. 

 MEDIAN PLANE - "middle" plane (of the em- 

 bryo). May be median sagittal or median 

 frontal. 

 MEDULLARIN - a sex differentiating substance 



spread in some annphibia by the blood stream 

 as a hornnone, and in other forms by dif- 

 fusion (see corticin). 

 MELANOBLAST - prospective pigment cell 



which will bear melanin (Ehrmann, 1896) 

 but confused by some authors to include 

 any pigment synthesizing cell. May be 

 present and yet unable to develop pigment 

 (e. g. , white axolotl). 

 MELANOKINS - stimuli which act upon melano- 

 phores, such as temperature, humidity, 

 light, hormones, and certain pharmacolog- 

 ical agents (Bytinski-Salz, 1938). 

 MELANOPHORES - cell with brown or black 

 (melanin) pigment granules or rods, found 

 in every class of vertebrates. Derived 

 from the neural crests and migrating 

 throughout the body. 

 MELANOPHORE, ADEPIDERMAL - dermal 



melanophore. 

 MELANOPHORES, DEPENDENT - dermal mel- 

 anophores (e. g. , in white axolotl) which 

 will develop pigment only under the influ- 

 ence of overlying transplanted pigmented 

 epidermis. (Du Shane, 1943.) 

 MEMBRANOUS CELL TYPE - fan-like protub- 

 erances of isolated embryonic cells, having 

 serrated pseudopodia (Holtfreter, 1943). 

 MEMBRANE, DESEMET'S - thinned out ecto- 

 derm of the cornea which occurs in res- 

 ponse to the contact of the developing optic 

 cup. 

 MEMBRANE, FERTILIZATION - a membrane 

 representing either the elevated vitelline 

 membrane or a newly formed membrane 

 found at the surface of an egg immediately 

 upon fertilization or following artificial 

 parthenogenetic stimulation (activation); 

 generally considered an adequate criterion 



of successful activation ot the egg. First 

 seen by Fol (1876) on the starfish egg. 



MERISIS - growth by cell multiplication (in 

 plants). 



MEROGON - an egg fragment, generally with 

 incomplete nuclear components. 



MEROGONY - development of fertilized but 



enucleated egg fragments (Delage, 1899). 



MEROGONY, ANDRO - development of an egg 

 fragment which contains the sperm nucleus 

 only (Bataillon & Tchou-Su, 1934). This 

 may be accomplished by surgical removal 

 of the egg nucleus (as it is giving off its 

 polar body) or by irradiation damage of the 

 egg nucleus (e. g. , androgenesis). 



MEROGONY, DIPLOID - fragment of an egg 



developing under the influence of the normal 

 diploid nucleus. 



MEROGONY, DOUBLE - cases where both halves 

 of an egg develop following fertilization, one 

 with a diploid fusion nucleus and the other 

 with an haploid sperm nucleus (Dalcq, 1932). 



MEROGONY, GYNO - the development of a 



fragment of a fertilized egg which fragment 

 contains the egg nucleus only. 



MEROGONY, PARTHENOGENETIC - develop- 

 ment of a fragment of an unfertilized egg 

 containing the egg nucleus and activated by 

 artificial means (E. B. Harvey, 1935). 



MEROGONY, PARTHENOGENETIC GYNO - 

 fragment of an egg containing the egg nu- 

 cleus only, stimulated to develop by artifi- 

 cial means. 



MEROMORPHOSIS - the new part regenerated is 

 less than the part removed. 



MESENDODERM - newly formed layer of 



(Urodele) gastrula before there has been 

 separation of endoderm and mesoderm, 

 group of cells lying posteriorly to the lip 

 of the blastopore, invaginated during gas- 

 trulation. Syn. , mesentoblast, ento-meso- 

 blast. 



MESENCHYME - the form of embryonic meso- 

 derm or mesoblast in which migrating cells 

 unite secondarily to form a syncitium or 

 network having nuclei in thickened nodes 

 between intercellular spaces filled with 

 fluid. Often derived from mesothelium. 



MESIAL - Syn. , median, medial, middle. 



MESODERM - primary germ layer which arises 

 from the marginal zone to take up its 

 assigned position between the outer ecto- 

 derm and the inner endoderm. 



MESOMERE - cells of intermediate size when 

 there are cells of various sizes (macro- 

 meres and micromeres being the largest 

 and the smallest, respectively). Also used 

 as synonym for intermediate cell mass 

 which gives rise to the nephric system. 



METABOLISM - the sum total of chemical 



changes occurring in the life of an organ- 

 ism. 



