GLOSSARY 461 



DIFFERENTIATION, CELLULAE - the process which results In specialization of a cell as measured by its dis- 

 tinctive, actual, and potential functions (Bloom, 1937) • 



DIFFERENTIATION CENTER - one of the true organization centers in the developing insect egg. Syn., dif- 

 ferenzier^ingszentrum (of Lehmann, 19'*'2). 



DIFFERENTIATION, CORPORATIVE - differentiation resulting from the physiological functioning of parts. 



DIFFERENTIATION, DEPENDENT - all differentiation that la not self-differentiation; the development of 

 parts of the organism under mutual Influences, such Influences being activating, limiting, or in- 

 hibiting. Inability of parts of the organism to develop Independently of other parts. Such a period 

 in ontogeny always precedes that of Irreversible determination. "Experimental embryology is a study 

 of the differentiations which are dependent, causally effected." (Roux, 1912). Syn., correlative 

 differentiation, Abhflnglge Dlfferenzlerung, Differentiation provoquee. 



DIFFERENTIATION, FITNCTIONAL - differentiation of tissues resulting from forces associated Vlth functions 

 (stresses and strains) which they are performing. 



DIFFERENTIATION, INDIYIDUATIVE - differentiation due to the action of morphogenetlc fields rather than to 

 physiological functioning of parts; opposed to corporative differentiation. 



DIFFERENTIATION POTENCY - the total repertoire of tllfferentiations, cytological and histological, avail- 

 able to a given cell. Wider significance than prospective fate. 



DIFFERENTIATION, REGIONAL - refers to fact that different parts of the organizer will induce different 

 end organ formation; also refers to organ districts In a (limb) field. 



DIFFERENTIATION, SELF - the perseverance in a definite course of development of a part of an embryo, re- 

 gardless of its altered surroundings (Roux, 1912). Syn., differentiation spontanee. 



DIKENETIC - dicentric, having two klnetochores. 



DIMEGALY - possessing spermatozoa of two sizes. 



DIPHYGENIC - having two types of development. 



DIPLICHRCMOSOIE - two identical chromosomes, held together at the kinetochore and originated by doubling 

 of chromosomes without separation of daughter chromosomes. 



DIPLOID - normal number of chromosomes, double the gametic or haploid; complete set of paired chromosomes 

 as in the fertilized egg or somatic cell. 



DIPYGUS - (See dupllcatus inferior.) 



DISSOGENY - having two sexually mature periods, one as a larva and one as an adult. 



DISTRICT - a portion of a morphogenetlc field with certain specific determinations. Syn., terrltolre. 



DIVERGENCE, VEMTEAL - divergence of material from the mid-ventral line, compensatory to the process of 

 dorsal convergence in gastrulation (Vogt). 



DIVISION HEIRAECHY - "four dimensional array of cells of which one and only one member (the zygote) is 



before all other members In time, and Is the only one to which every other term stands in a relation 

 which is some power of D (i.e., the relation is Dpo)." (Bertelanffy & Woodger, 1953.) 



DOMINANCE - in embryology this term refers to parts of a system which have greater growth momentum and 

 also which gather strength from the rest, such as the dorsal blaetoporal lip. 



DOWNAN EQUILIBRIUM - distribution of ions on two sides of a semi -permeable membrane with diffusion until 



concentration of diffusible ions on the two sides of the membrane is the same, involving ionic rather 

 than molecular balance. 



DOPA - 3:lt:dloxyphenylalanin, ein intermediate oxidation product of tyrosine and one that appears as a 

 precursor of melanin pigment in mammals (Black, 1917). 



DOESO-VEMTRAL - orientation of a graft or transplant so that the original dorsal-ventral axis is Inverted 

 in relation to the host field. 



D-QUADRANT - one of the four early blastomeres of the annelid embryo which has the prospective function 

 of giving rise chiefly to mesoderm. 



DOUBLE ASSURANCE - cases where inductions usually occur but are not absolutely necessary; two processes 

 working together, either one of which would be sufficient to accomplish the end result. Ability to 

 bring about a morphogenetlc process by means other than the usual one, (e.g., 'removal of the eye 

 cup in R. esculenta and the overlying ectoderm will form a lens anyway, without the normal Inducing 

 Influences of the eye cup). Term used by Rhumbler (1897) in connection with cell division and by 

 H. Braus (1906) in development. Syn., doppelte sicherung. 



DUPLICITAS CRUCIATA - double monsters, obtained by grafting or by inversion of the 2-cell amphibian embryo. 



DUPLICITAS INFERIOR - conjoined twins fused anteriorly, having two rumps. Syn., dipygus. 



DYSMEROGENESIS - cleavage resulting in unlike parts. 



DYSPLASTIC TREATMENT - introduction of a transplant from organism of a different phylum. (E.g., frog to 

 mammal or vice versa. ) 



DYSTELEOLOGY - apparent lack of purpose in organic processes or structures although they may ultimately 

 be shown to be teleological. 



ECDYSIS - process of moulting a cuticular layer, shedding of epithelium by amphibia. 



ECHINOCHROME - red pigment of Echlnoderm eggs which probably has respiratory function. 



ECTODERM - the outermost layer of a didermic embryo (gastrula). Syn., epiblast. 



ECTOPIC - out of Its normal position, used in connection with transplants. 



ECTOPLASM - external layer of protoplasm of the (egg) cell, the layer immediately beneath the cell mem- 

 brane. Seat of Lillle's fertilizin and of all developmental processes, according to Just. Syn., 

 egg cortex plasmalemma. 



EGG, ALECITHAL - eggs with little or no yolk. 



EGG, CLEIDOIC - egg which is covered by a protective shell (e.g., eggs of reptiles, birds, and oviparous 

 mammals ) . 



