268 GLOSSARY OF EMBRYOLOGICAL TERMS 



Chromophobe — cells whose constituents are non-stainable; have no affinity 

 for dyes. 



Chromosome — chromatic or deeply staining bodies derived from nuclear 

 network and containing a matrix and one or more chromonemata dur- 

 ing process of mitosis; bodies found in all somatic cells of normal 

 organism in a number characteristic of the species; bearers of gene. 



Cleavage — mitotic division of egg resulting in blastomeres. (Syn., segmenta- 

 tion. ) 



Cleavage, Accessory — cleavage in peripheral or deeper portions of (chick) 

 germinal disc caused by supernumerary sperm nuclei following (nor- 

 mal) polyspermy, sometimes occurring in urodeles. 



Cleavage, Asymmetrical — extremely unequal divisions of egg as in Cteno- 

 phore. 



Cleavage, Bilateral — cleavage in which egg substances are distributed sym- 

 metrically with respect to median plane of future embryo. 



Cleavage, Determinate — cleavage in which certain parts of future embryo 

 may be circumscribed in certain specific (early) blastomeres; cleavage 

 which produces blastomeres that are not qualitatively equipotential, 

 i.e., when such blastomeres are isolated they will not give rise to 

 entire embryos. (Syn., mosaic development.) 



Cleavage, Dexiotropic — cleavage resulting in a right-handed production 

 of daughter blastomere(s), as in spiral cleavage. 



Cleavage, Discoidal — See Cleavage, Meroblastic. 



Cleavage, Equatorial — cleavage at right angles to egg axis, opposed to 

 vertical or meridional; often the typical third cleavage plane. (Syn., 

 latitudinal or horizontal cleavage.) 



Cleavage, Holoblastic — complete division of egg into blastomeres, gen- 

 erally equal in size although not necessarily so (e.g., Amphioxus). 

 (Syn., total cleavage.) 



Cleavage, Horizontal — See Cleavage, Equatorial. 



Cleavage, Indeterminate — cleavage resulting in qualitatively equipotential 

 blastomeres in early stages of development. When such blastomeres 

 are isolated from each other they give rise to complete embryos. Op- 

 posed to mosaic development. (Syn., regulatory development.) 



Cleavage, Latitudinal — See Cleavage, Equatorial. 



Cleavage Laws — See specific laws under names of Balfour, Hertwig, and 

 Sachs. 



