1*58 GLOSSARY 



CHEOMOSOME - the chromatic or deeply staining bodies derived from nuclear network, which are conspicuous 

 during mitotic cell division and which are represented in all of the somatic cells of an organism In 

 a number characteristic for the species; bearers of the genes. 



CHROMOSOME ABEREATION - an Irregularity in the constitution or the number of chromosomes which may pro- 

 duce modifications in the normal course of development. 



CHEOMOSOMIN - acidic protein, present In nuclei, considered an essential part of the chromosomes (Stedman, 

 19''5). 



CLEAVAGE - the mitotic division of an egg resulting in blastomeres. Syn., segmsntation. 

 'CLEAVAGE, ACCESSOEY - cleavages in peripheral or deeper portions of the (chick) germinal disc caused by 

 supernumerary sperm nuclei following (normal) polysperny. 



CLEAVAGE, ASYMMETRICAL - extremely unequal divisions of the egg aa In Ctenophores. 



CLEAVAGE, BILATERAL - cleavage in which the egg substances are distributed symmetrically with respect to 

 the median plane of the future embryo. 



CLEAVAGE, DETERMINATE - cleavage in which certain parts of the future embryo may be circumscribed In cer- 

 tain specific (early) blastomeres; cleavage which produces blastomeres that are not qualitatively 

 equlpotential, (i.e., when such blastomeres are isolated they will not give rise to entire embryos). 

 The early embryo is a mosaic of qualitatively different blastomeres with respect to further ontogeny. 



CLEAVAGE, DEXIOTROPIC - cleavage resulting In a right-handed production of daughter bla8tomere(s), as In 

 some cases of spiral cleavage. 



CLEAVAGE, DISCOIDAL - cell division restricted to a more-or-less circular disc of protoplasm to one side 

 of a relatively enormous mass of yolk (e.g., chick egg). Syn., meroblastic cleavage. 



CLEAVAGE, EQUATORIAL - cleavage at right angles to the egg axis, opposed to vertical or meridional. 

 Often the third cleavage plane. Syn., latitudinal or horizontal cleavage. 



CLEAVAGE, HOLOBLASTIC - complete division of the egg into blastomeres, generally equal in size (Asterlas, 

 Arbacia) although not necessarily so (Amphloxus, Frog). Syn., total cleavage. 



CLEAVAGE, HORIZONTAL - (See cleavage, equatorial.) 



CLEAVAGE, INDETERMINATE - cleavage resulting in qualitatively equl -potential blastomeres in the early 

 stages of development. When such blastomeres are Isolated from each other they tend to give rise 

 to complete embryos. Opposed to mosaic development. Syn., regulatory cleavage, or development. 



CLEAVAGE, LATITUDINAL - (See cleavage, equatorial.) 



CLEAVAGE LAWS - (See specific laws under names of Balfour, Hertwlg, and Sachs.) 



CLEAVAGE, LEVOTEOPIC - cleavage resulting In left-handed or counter-clockwise production of daughter 

 bla3tomere( 3) as In some cases of spiral cleavage. 



CLEAVAGE, MERIDIONAL - cleavage along the egg axis, opposed to equatorial. Generally the first two 

 cleavages of any egg. Syn., vertical cleavage. 



CLEAVAGE, MEROBLASTIC - (See discoldal cleavage.) 



CLEAVAGE NUCLEUS - the nucleus which controls cleavage. This may be the syngamlc nucleus of normal 

 fertilization; the egg nucleus of parthenogenetlc or gynogenetlc eggs; or the sperm nucleus of 

 androgenetic development. 



CLEAVAGE PATH - path taken by the syngamlc nucleus to the position awaiting the first division. 



CLEAVAGE, RADIAL - holoblastlc cleavage which results in (two) super-imposed tiers of cells as early as 

 the 8-oell stage. Opposed to spiral cleavage. 



CLEAVAGE, SPIRAL - cleavage at an oblique angle with respect to the egg axis so that the resulting blas- 

 tomeres (generally upper mlcromeres at the 8-cell stage) lie in an interlocking fashion within the 

 furrows of the original blastomeres. The shift In expected position is due to intrinsic genetic 

 factors rather than external pressure, (e.g., Mollsuca.) Opposed to radial cleavage. 



CLEAVAGE, SUPERFICIAL - cleavage around the periphery of centrolecithal eggs. Syn., peripheral cleavage. 



CLEIDOIC - refers to eggs that are more-or-less closed off from their environment (e.g.. Chick). 



CLINOSTAT - apparatus for keeping objects In constant rotation. 



COADAPTATION - correlated variation in two mutually dependent organs. 



COELOBLASTULA - spherical ball of cells (blastomeres) developing in early cleavage as a result of segmen- 

 tation, provided with a large central cavity (blastocoel) . (e.g., Echlnodermata. ) 



COELCM - mesodermal body cavity of chordates, from the walls of which develop the gonads. It Is sub- 

 divided in higher forms Into pericardial, pleural, and peritoneal cavities. Extended as the exocoel 

 or extra embryonic body cavity of chick embryo. 



COENOBLAST - the layer which will give rise to the endoderm and mesoderm (obsolete). 



COLLOID - dispersed substance whose particles are not smaller than lu nor larger than 100)i, approximately. 

 Physical state of protoplasm. 



COLORLESS PIGMENT CELL - same as dependent or potential pigment cell of DuShane and Hamilton. Syn., 

 farbloae plgmentzellen. 



COMPETENCE - state of reactivity, of dis-equlllbrium In a complex system of reactanta. Possessing labile 

 determination (Reaklonafahlg) or having reaction possibility (Raven). Competencies may appear 

 simultaneously or \n sequence within a given area, some to disappear later even without function. 

 Embryonic competence seems to be lost in all adult tissues but may be reclaimed in a blastema. It is 

 a name for the state of the cell area at or before the time when irritability is resolved and a 

 developmental path is chosen. The word supercedes the older words of "potence", "potency", or 

 "potentiality" ' 



COMPRESSION - either the acceleration of development or the extension of a certain (e.g., pre-hatchlng) 

 period, resulting in the completion (or omission) of certain (larval) stages, in an unbalanced time 

 schedule. 



