GLOSSARY OF EMBRYOLOGICAL TERMS 267 



Chimera — compound embryo generally derived by grafting major portions 

 of two embryos, usually of different species; may be derived by ab- 

 normal chromosome distribution in cleavage after normal fertiliza- 

 tion. 



Choana — openings of olfactory organ into pharynx, internal nares. Some- 

 times also used in connection with external olfactory opening. 



Chondrification — process of forming cartilage, by secretion of a homoge- 

 neous matrix between the more primitive cells. 



Chondrin — chemical substance in cartilage which makes it increasingly 

 susceptible to basic stains. 



Chondrocranium — that portion of skull which is originally cartilaginous. 



Chorda Dorsalis — Syn., notochord. 



Chorda Mesoderm — region of the late (amphibian) blastula, arising from 

 gray crescent area, which will give rise to notochord and mesoderm and 

 will, if transplanted, induce formation of secondary medullary folds. 



Choroid Coat — mesenchymatous and sometimes pigmented coat within 

 sclerotic coat but surrounding pigmented layer of eye in vertebrate 

 embryos. 



Choroid Fissure — inverted groove in optic stalk whose lips later close 

 around blood vessels and nerves that enter eyeball. 



Choroid Knot — thickened region of fused lips of choroid fissure, near 

 pupil, from which arise cells of iris. 



Chromatid — one of the parts of a tetrad (McClung, 1900); really a longi- 

 tudinal half of a chromosome. 



Chromatin — deeply staining substance of nuclear network and chromo- 

 somes, consisting of nuclein; gives Feulgen reaction and stains with 

 basic dyes. 



Chromatophore — pigment-bearing cell frequently capable of changing size, 

 shape, and color; cells responsible for superficial color changes in 

 animals; behavior under control of sympathetic nervous system or 

 neurohumors. 



Chromidia — granules within cytoplasm which stain like chromatin and 

 which may actually be extruded chromatin granules. 



Chromomere — unit of chromosome recognized as a chromatin granule. 



Chromonema — slender thread of chromatin which is core of chromosome 

 during mitosis. 



Chromophil — cells which have an affinity for dyes. 



