GLOSSARY OF EMBRYOLOGICAL TERMS 263 



Aqueous Humor — fluid which fills anterior and posterior chambers of eye 

 between lens, probably derived from mesoderm. 



Archencephalon — pre-chordal brain, e.g., forebrain. Brain anterior to an- 

 terior end of notochord. 



Archenteric Pouch — See Enterocoel. 



Archenteron — primitive gut found in gastrula and communicating with out- 

 side by blastopore; precursor of embryonic gut. (Syn., gastrocoel, 

 enteron.) 



Arcualia — small blocks of sclerotomal connective tissue involved in forma- 

 tion of vertebrae. 



Asexual Reproduction — reproduction without union of gametes; generally 

 with no maturation divisions. 



Aster — "star-shaped structure" surrounding centrosome (Fol, 1877); lines 

 radiating in all directions from centrosome during mitosis. 



Astral Rays — lines which make up aster. 



Astrocytes — stellate-shaped cells arising from spongioblasts of mantle layer, 

 classified under the more general term of neuroglia. 



Atrium — two upper chambers of frog's embryonic heart, later to be known 

 as auricles. 



Attachment Point — point of chromosome to which spindle fiber is attached 

 and therefore portion of chromosome nearest centrosome in anaphase. 

 (Syn., centrosome, chromocenter, kinetochore.) 



Attraction Sphere — See Centrosphere. 



Auricles — two upper chambers of adult frog's heart, derived from em- 

 bryonic atria. 



Autogamy — self-fertilization. 



Autosome — any chromosome except so-called sex (X or Y) chromosomes. 



Auxocyte — pre-meiotic germ cell. (Syn., primary cyte, meiocyte.) 



Axial Filament — central fiber in tail of a spermatozoon. 



Axial Mesoderm — that portion of epimeric mesoderm nearest notochord. 

 (Syn., vertebral plate.) 



Axis — imaginary central or median line, generally correlated with a gradient. 



Axis of the Cell — imaginary line passing through centrosome and nucleus 

 of a cell, generally also through geometrical center of cell. In an egg 

 such an axis generally is also gradient axis of materials such as cyto- 

 plasm, yolk, pigment, etc. 



