GLOSSARY 1*59 



CONCBESCENCZ - the coming together of previously separate parts (cell areas) of the embryo, generally re- 

 sulting In a piling up of parts. One of the corollaries of gastrulation where a bottle-neck of cell 

 movements occurs at the lips of the blastopore. Original meaning (His, IST"*) referred to presumed 

 pre-formed parts of the fish germ ring. (See confluence.) 



CONE, EXUDATION - (See cone fertilization.) Term used by Fol, 1879. 



CONE, FEETILIZATION - a conical projection of the cytoplasm from the surface of the egg to meet the 



spermatozoon which is to invade the egg cortex. The cone makes contact and then draws the sperm in- 

 to the egg. Not universally demonstrated but seen in the starfish (Chambers). Syn., exudation cone. 



CONES OF GBOWTH - the enlarged outgrowth of the neuroblast forms the axis cylinder or axone of the nerve 

 fiber and is termed the cone of growth because the growth processes by which the axone Increases in 

 length are supposed to be located there. 



CONFLUENCE - similar to concrescence except that this term refers specifically to the "flow" of cells 

 (or cell areas) together, without presumption of any organ preformation. Said areas have certain 

 potentialities in unaltered normal development. (See concrescence.) 



CONSTBICTION - gradual closure of the blastopore (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 Konzentrlsches Urmundschluss of Vogt. 



CONVEEGENCE, DORSAL - material of the marginal zone moves toward the dorsal mid-line as it involutes and 

 invaglnates during gastrulation, resulting in a compensatory ventral divergence. Syn., confluence 

 of Smith or dorsal Eaffung of Vogt. 



CORDS, MEDULLARY - structures which give rise to the urogenital connections and take part in the forma- 

 tion of the seminiferous tubules, and are derived from the blastema of the mesonephrlc cords 

 (amphibia). 



CORDS, SEX - strands of somatic cells and primordial germ cells growing from the cortex toward the medulla 

 of the gonad prlmordium. Best seen in early phases of testes development. 



CORRELATION COEFFICIENT - correlation of growth rates of different parts (of embryo). 



COETICIN - sex differentiating substances spread in some amphibia by the blood stream and in other forms 

 by diffusion, acting as a hormone. (See medullarln. ) 



CRANIAL - relative to the head; "cranlad" means toward the head. Syn., rostral, cephalad. 



CEANIOPAGUS - cranial union in conjoined twins. 



CRANIOSCHISIS - open- roofed skull associated with undeveloped brain. Syn., acranla. 



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 pigment away from the area and to- 

 ward the sperm entrance point (Eoux, 1888) which Is therefore opposite; region of the presumptive 

 chorda-mesoderm, the future blastopore and anus. 



CRESCENT, YELLOW - crescentic area on the surface of the (Aecldian) 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 Integu- 

 ment. 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; exaggeration of the vegetatlviza- 

 tlon tendencies. 



CYTARME - flattening of previously rounded blastomerea against each other following the coii5)letlon 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 cyto- 

 plasm around them to divide. Activity and structure unrelated to chromosomal material. 



CYTE - a suffix meaning "cell" as oo-cyte (egg forming cell), spermato-cyte (sperm forming cell), or 

 osteo-cyte (bone forming cell). (See specific definitions.) 



CYTOCHORISMUS - apparent partial separation of the blastomeres at the flat, previously continuous sur- 

 face (Eoux). 



CYTOCHRCME - an oxldlsable pigment found in nearly all cells exhibiting definite spectral bands in re- 

 duced form, discovered by Kellin (1925). Insoluble in water, poisoned by HON, COg, and 1^3. 



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, I89I*). 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 cytoteucls). Crawling, amoeboid movement similar to chemotaxis (Roux). May also Include 

 repulsive movements of cell groups (negative cytotaxis). 



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). 



