GLOSSARY 



471 



CERVICAL CYST - imperfect occlusion of a 



branchial (2nd) cleft. Syn. , branchial cyst. 



CERVICAL FISTULA - incomplete closure of 

 the branchial cleft. 



CHALONES - internal secretions with depress- 

 ing effects, opposed to hormones. 



CHEMO-NEUROTROPISM - chemical attraction 

 of degenerating nerve upon regenerating 

 nerve fibers. The chemical nature of nerve 

 orientation (growth and connections) de- 

 pending upon diffusing substances which 

 seem to attract nerve fibers. 



CHIMERA - compound embryo derived by graft- 

 ing together major portions of two embryos, 

 generally of different species; exchange of 

 parts too great to be called a transplant. 

 From Greek mythology: forepart a lion, 

 middle a goat, and hindpart a dragon. 



CHORDA-MESODERM - region of the dorsal 



lip of the blastopore, arising from the grey 

 crescent area, destined to give rise to 

 notochord and mesoderm in the amphibia. 



CHORIO-ALLANTOIS - a common membrane 

 formed by the fusion of the inner wall of 

 the chorion and the outer wall of the allan- 

 tois (chick), consisting of outer ectoderm, 

 intermediate fused mesodern:!, and inner 

 endoderm. 



CHORIO-ALLANTOIC GRAFT - graft from 

 various sources which, by virtue o'f its 

 weight and other factors, provides local 

 irritation of the chorio -allantoic membrane 

 of the chick so that the graft becomes vas- 

 cularized and surrounded by indifferent tis- 

 sue, offering the graft excellent conditions 

 for survival, growth, and differentiation. 

 Graft not incorporated by the host from 

 which it receives nutrition for growth. 



CHORION - an embryonic naembrane developed 

 in the chick as a corollary to the amnion; 

 encloses both the amnion and the allantois. 

 Never maternal in mammals. 



CHROMATID - longitudinal half of an anaphase, 

 interphase, or prophase chromosonne at 

 mitosis. One of four strands (in meiosis) 

 involved in crossing over and visible after 

 pachytene. Becomes a chromosome at 

 metaphase of the second (reduction) division. 



CHROMATIN - deeply staining substance of the 

 nuclear network and the chromosomes, con- 

 sisting of nuclein; gives Feulgen reaction 

 and stains with basic dyes. 



CHROMATOBLASTS - potential pigment cells 

 which, upon proper extrinsic stimulation, 

 will exhibit pigmentation. 



CHROMATOPHORE - pigment bearing cell fre- 

 quently capable of changing size, shape, and 

 color; responsible for superficial color 

 changes in many aninnals (e. g. , squid and 

 chameleon), under the influence of the sym- 

 pathetic nervous system and/or the neuro- 

 humors. 



CHROMIDIA - extra-nuclear granules of chromatin. 



CHROMONEMA - optically single thread within 

 the chromosome, a purely descriptive term 

 without functional implications. 



CHROMONU OLEIC ACID - one of the two types 

 of nucleic acid detected in chromatin only 

 (PoUister St Mirsky, 1944). Syn. , des- 

 oxyribose nucleoprotein, thymonucleic acid. 

 (See plasmonucleic acid. ) 



CHROMOPHOBE - cells whose constituents are 

 non-stainable; no affinity for dyes. 



CHROMOSOME - the chromatic or deeply stain- 

 ing 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 ABERRATION - an irregularity 

 in the constitution or the number of chromo- 

 somes which may produce modifications in 

 the normal course of development. 



CHROMOSOMIN - acidic protein, present in 



nuclei, considered an essential part of the 

 chromosomes (Stedman, 1945). 



CLEAVAGE - the mitotic division of an egg re- 

 sulting in blastomeres. Syn. , segmenta- 

 tion. 



CLEAVAGE, ACCESSORY - cleavages in peri- 

 pheral or deeper portions of the (chick) 

 germinal disc caused by supernumerary 

 sperm nuclei following (normal) polyspermy. 



CLEAVAGE, ASYMMETRICAL - extremely un- 

 equal divisions of the egg as in Ctenophores. 



CLEAVAGE, BILATERAL - cleavage in which 

 the egg substances are distributed symmet- 

 rically with respect to the median plane of 

 the future embryo. 



CLEAVAGE, DETERMINATE - cleavage in 

 which certain parts of the future embryo 

 may be circunnscribed in certain specific 

 (early) blastomeres; cleavage which pro- 

 duces blastomeres that are not qualitatively 

 equipotential, (i. e. , when such blastomeres 

 are isolated they will not give rise to entire 

 embryos). The early embryo is a rftosaic 

 of qualitatively different blastomeres with 

 respect to further ontogeny. 



CLEAVAGE, DEXIOTROPIC - cleavage result- 

 ing in a right-handed production of daughter 

 blastomere(s), as in some cases of spiral 

 cleavage. 



CLEAVAGE, DISCOIDAL - cell division re- 

 stricted to a more-or-less circular disc of 

 protoplasm to one side of a relatively enor- 

 mous 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. 



