1*70 GLOSSARY 



LUNAE PERIODICITY - maturation and ovl position during certain phases of the lunar cycle (e.g.. Nereis 

 llmbata sheds its gametes in the period from the full moon to the new moon in June to September). 



MACERATIOM - to swell by soaking. In water the connective tissue between cells is loosened and the 



cells tend to separate. 

 MACEOCEPHALUS - abnormally large head due to abnormal development of the cranium. Often the brain Is 



swollen with cerebrospinal fluid. Syn., hydrocephalus. 

 MACBOMERE - larger of the blastomeres where there is a conspicuous size difference, generally the yolk- 

 laden endoderm forming cells. Opposed to mlcromere. 

 MACB06QMIA - gigantism, enlarged skeleton due to disturbed function of the pituitary and possibly also 



the thyroid glands. 

 MACFOSTCMIS - failure of the primitive mouth slit to reduce normally. 

 MARGINAL BELT - ring of presumptive mesoderm of the amphibian blastula, essentially similar to the grey 



crescent of the undivided egg. 

 MATRIX - ground substance surrounding the chromonemata, usually less chromatic and mfiking up the body 



of the chronoeome. Syn., kalymma or hyalonema. 

 MATRIX, INTERCELLULAR - the cytoplasmic wall substance of cells in a whole blastema which forms an 



Integrated foam structure and, because of its continuity, shows a very definite syncitlal character. 



(Moore) „ 



MATURATION - the process of transforming a primordial germ cell (spermatogonium or oogonium) into a 



functionally mature germ cell, the process involving two special divisions, one of which is always 



meiotlc or reductlonal. 

 MAUTHEH'S FIBHK - two highly differentiated, giant neurones found in the medulla of teleost fishes and 



amphibia and possessing extensive dendritic connections; axones extend from VIII cranial ganglion 



through the spinal cord. The fibers are functional particularly in maintaining the sense of 



eq^uillbrlum and are Indlspensible 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 processes 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 embryo). May be median saglltal or median frontal. 

 MEDULLARIN - a sex differentiating substance spread in some amphibia by the blood stream as a hormone, 



and in other forms by diffusion (see cortlcln). 

 MELANOBLAST - prospective pigment cell which will bear melanin (Ehrmann, I896) but confused by some 



authors to Include any pigment synthesizing cell. May be present and yet unable to develop pig- 

 ment (e.g., white axolotl). 

 MELANOKINS - stimuli which act upon melanophores, such as temperature, humidity, light, hormones, and 



certain pharmacological agents (Bytlnski-Salz, 1958). 

 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. 

 MELANOPHOEE, ADEPIDERMAL - dermal melanophore. 

 MELANOPHORES, DEPENDENT - dermal melanophores (e.g., In white axolotl) which will develop pigment only 



under the influence of overlying transplanted pigmented epidermis. ( Du Shane, 19'*3.) 

 MEMBRANOUS CELL TYPE - fan-like protuberances of Isolated embryonic cells, having serrated pseudopodla 



(Holtfreter, 19't5). 

 MEMBRANE, DESEMET'S - thinned out ectoderm of the cornea which occurs in response 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 arti- 

 ficial parthenogenetlc stimulation (activation); generally considered an adequate criterion of 



successful activation of the egg. First seen by Fol (I876) 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). 

 MEEOGONY, ANDRO - development of an egg fragment which contains the sperm nucleus only (Batalllon & 



Tchou-Su, 195'*). 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., androgenesls) . 

 MEBOGONY, 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 - development of a fragment of an unfertilized egg containing the egg nucleus 



and activated by artificial means (E. B. Harvey, 1935). 

 MEBOGONY PABTHENOGENETIC GYNO - fragment of an egg conteilning the egg nucleus only, stimulated to develop 



by artificial 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 gae- 



trulatlon. Syn., mesentoblaat, ento-mesoblast. 



