270 GLOSSARY OF EMBRYOLOGICAL TERMS 



Columella — bone in tubo-tympanic cavity of frog which aids in auditory 

 sensations. (Syn., plectrum, malleus.) 



Competence — ability of embryonic area to react to stimulus (e.g., evo- 

 cator). 



Concrescence — coming together of previously separate parts (cell areas) 

 of embryo, generally resulting in a piling up of parts. One of the 

 corollaries of gastrulation where a bottle-neck of cell movements 

 occurs at lips of blastopore. Original meaning (His, 1874) referred 

 to presumed preformed parts of fish germ ring. (See Confluence.) 



Cone, Fertilization — conical projection of cytoplasm from surface of egg 

 to meet spermatozoon which is to invade egg cortex. Cone makes 

 contact and then draws sperm into egg. Not universally demonstrated 

 or seen in frog, but seen in starfish (Chambers). (Syn., exudation 

 cone.) 



Cones of Growth — enlarged outgrowth of neuroblast forms axis cylinder 

 or axon of nerve fiber and is termed cone of growth because growth 

 processes by which axon increases in length are supposed to be 

 located there. 



Confluence — similar to concrescence except that this term refers specifi- 

 cally to "flow" of cells (or areas) together, whether or not they are 

 piled up. 



Constriction — gradual closure of blastopore (diametrical reduction of 

 germ ring) over yolk toward vegetal pole. May be due to stretching 

 of marginal zone, to pull or tension of dorsal lip, or even to narrow- 

 ing of marginal zone. (Syn., convergence [Jordan] or Konzentrisches 

 Urmundschluss [Vogt].) 



Convergence, Dorsal — material of marginal zone moves toward dorsal 

 mid-line as it involutes during gastrulation, resulting in a compensa- 

 tory ventral divergence. (Syn., confluence [Smith] or dorsal Reffung 

 [Vogt].) 



Copulation Path — second portion of sperm migration path through egg 

 toward egg nucleus, when there is any deviation from entrance or 

 penetration path; path of spermatozoon which results in syngamy. 



Cords, Medullary — structures which give rise to urogenital connections 

 and take part in formation of seminiferous tubules, and are derived 

 from blastema of mesonephric cords. 



Cords, Sex — strands of somatic cells and primordial germ cells growing 

 from cortex toward medulla of gonad primordium. Best seen in early 

 stages of testes development. 



