GLOSSARY 



473 



CONFLUENCE - similar to concrescence ex- 

 cept that this term refers specifically to 

 the "flow" of cells (or cell areas) together, 

 without presumption of any organ prefor- 

 mation. Said areas have certain potential- 

 ities in unaltered normal development. 

 (See concrescence. ) 



CONSTRICTION - gradual closure of the blasto- 

 pore (germ ring) over the yolk toward the 

 vegetal pole. May be due to stretching of 

 the marginal zone, to a pull or tension of 

 the dorsal lip, or even to the narrowing of 

 the marginal zone. Syn. , convergence of 

 Jordan or Konzentrisches Urmundschluss 

 of Vogt. 



CONVERGENCE, DORSAL - material of the 

 marginal zone moves toward the dorsal 

 mid-line as it involutes and invaginates 

 during gastrulation, resulting in a com- 

 pensatory ventral divergence. Syn. , con- 

 fluence of Smith or dorsal Raffung of Vogt. 



CORDS, MEDULLARY - structures which give 

 rise to the urogenital connections and take 

 part in the formation of the seminiferous 

 tubules, and are derived from the blastema 

 of the mesonephric cords (amphibia). 



CORDS, SEX - strands of somatic cells and 

 primordial germ cells growing from the 

 cortex toward the medulla of the gonad pri- 

 mordium. Best seen in early phases of 

 testes development. 



CORRELATION COEFFICIENT - correlation of 

 growth rates of different parts (of embryo). 



CORTICIN - sex differentiating substances 



spread in some amphibia by the blood stream 

 and in other forms by diffusion, acting as a 

 hormone. (See meduUarin. ) 



CRANIAL - relative to the head; "craniad" means 

 toward the head. Syn. , rostral, cephalad. 



CRANIOPAGUS - cranial union in conjoined 

 twins. 



CRANIOSCHISIS - open-roofed skull associated 

 with undeveloped brain. Syn. , acrania. 



CRESCENT, GREY - crescentic area between 



the original animal and vegetal hemispheres 

 on the surface of the (frog) egg, grey in 

 color because of the migration of black pig- 

 ment away from the area and toward the 

 sperm entraince point (Roux, 1888) which is 

 therefore opposite; region of the presump- 

 tive chorda-me-soderm, the future blasto- 

 pore and anus. 



CRESCENT, YELLOW - crescentic area on the 

 surface of the (Ascidian) egg, yellow in 

 color. Gives rise to the mesoderm of such 

 embryos. 



CREST, NEURAL - paired cell masses derived 

 from ectoderm cells along the edge of the 

 former neural plate, and wedged into the 

 space between the dorso-lateral wall of the 

 closed neural tube and the integument. Gives 



rise to spinal ganglia after segmentation. 



CREST SEGMENT - the original neural crests 

 which become divided into segments, with 

 the aid of the somites, from which develop 

 the spinal and possibly also some cranial 

 ganglia. 



CROSS -FERTILIZATION - union of gametes 



produced by different individuals which, if 

 they are of different species, may produce 

 hybrids with variable viability. 



CYCLOPIA - failure of the eyes to separate; 



median fusion of the eyes which may be due 

 to suppression of the rostral block of tissue 

 which ordinarily separates the eyes; exag- 

 geration of the vegetativization tendencies. 



CYTARME - flattening of previously rounded 

 blastomeres against each other following 

 the completion of cleavage. 



CYTASTERS - asters arising independently of 

 the nucleus in the cytoplasm. May contain 

 centrosomes, and achromatic figure with 

 attraction sphere and astral rays and may 

 divide and even cause the cytoplasm around 

 thenn to divide. Activity and structure un- 

 related to chromosomal material. 



CYTE - a suffix meaning "cell" as oo-cyte (egg 

 forming cell), spermato-cyte (sperm form- 

 ing cell), or osteo-cyte (bone forming cell). 

 (See specific definitions. ) 



CYTOCHORISMUS - apparent partial separation 

 of the blastomeres at the flat, previously 

 continuous surface (Roux). 



CYTOCHROME - an oxidizable pigment found 

 in nearly all cells exhibiting definite spec- 

 tral bands in reduced form, discovered by 

 Keilin (1925). Insoluble in water, poisoned 

 by HCN, CO2, and H2S. 



CYTOLISTHESIS - tendency of embryonic cells 

 to aggregate and to fill up disruptions of 

 their union even in the absence of a common 

 surface membrane, due to surface tension 

 and selective adhesiveness (Roux, 1894). 

 Moving of cells over one another by sliding, 

 rotation, or both processes. 



CYTOLYSIS - breakdown of the cell, indicated 

 by dispersal of formed components. 



CYTOSOME - cytoplasmic mass exclusive of 

 the nucleus. 



CYTOTAXIS - coming together of (amphibian) 

 blastula cells after being teased apart in 

 salt solution (positive cytotaxis). Crawl- 

 ing, amoeboid movement similar to chemo- 

 taxis (Roux). May also include repulsive 

 movements of cell groups (negative cyto- 

 taxis). 



CYTOLEOSIS - process by which a cell, already 

 irreversibly differentiated, proceeds to its 

 final specialization (Hoadley). 



CYTOTROPISM - inevitable movement of a cell 

 in response to external forces (Rhumbler, 

 1899). 



