GLOSSARY OF EMBRYOLOGICAL TERMS 269 



Cleavage, Levotropic — cleavage resulting in left-handed or counterclock- 

 wise production of daughter blastomere(s) as in some cases of spiral 

 cleavage. 



Cleavage, Meridional — cleavage along egg axis, opposed to equatorial; 

 generally the first two cleavages on any egg. (Syn., vertical cleavage.) 



Cleavage, Meroblastic — cleavage restricted to peripherally located proto- 

 plasm, as in chick egg. (Syn., discoidal cleavage.) 



Cleavage Nucleus — nucleus which controls cleavage. This may be syn- 

 gamic nucleus of normal fertilization, egg nucleus of parthenogenetic 

 or gynogenetic eggs, or sperm nucleus of androgenetic eggs. 



Cleavage Path — path taken by syngamic nuclei to position awaiting first 

 division. 



Cleavage, Radial — holoblastic cleavage which results in tiers of cells. 



Cleavage, Spiral — cleavage at an oblique angle with respect to egg axis so 

 that resulting blastomeres (generally micromeres) lie in an interlock- 

 ing fashion within furrows of original blastomeres, due to intrinsic 

 genetic factors (e.g., Mollusca). 



Cleavage, Superficial — cleavage around periphery of centrolecithal eggs. 

 (Syn., peripheral cleavage.) 



Cochlea — portion of original otic vesicle associated with sense of hearing; 

 supplied by vestibular ganglion of eighth cranial nerve, having to do 

 with equilibration. 



Coeloblastula — spherical ball of blastomeres with a central cavity (e.g., 

 Echinoderms). 



Coelom — mesodermal cavity from walls of which gonads develop; cavity 

 subdivided in higher forms into pericardial, pleural, and peritoneal 

 cavities. (Syn., extra-embryonic body cavity and exocoel.) 



Coitus — copulation of male and female, term generally used in connec- 

 tion with mammals. Comparable situation in amphibia is called 

 amplexus. 



Collecting Tubule — portion of nephric tubule system leading to nephric 

 duct (Wolffian, etc.); term also used to refer to tubules which con- 

 duct spermatozoa from seminiferous tubule to vasa efferentia, within 

 testis. 



Colloid — dispersed substance whose particles are not smaller than 1 ^ 

 and not larger than 100 jx, approximately. Physical state of proto- 

 plasm. 



