GLOSSARY OF EMBRYOLOGICAL TERMS 281 



Gonoduct — See Genital Ducts. 



Gradient — gradual variation of developmental forces along an axis; scaled 

 regions of preference. (See Axis.) 



Gray Crescent — See Crescent, Gray. 



Growth — developmental increase in total mass of protoplasm at expense of 

 raw materials; an embryonic process, generally differentiation; cell 

 proliferation. 



Gynogenesis — development of sperm activated egg but without benefit of 

 sperm nucleus. 



Haploid — having a single set of chromosomes not appearing in allelo- 

 morphic pairs, as in mature gametes. Opposed to diploid, or the con- 

 dition in somatic cells. 



Harmonious-Equipotential System — embryonic system in which all parts 

 are equally ready to respond to organism as a whole. Isolated blas- 

 tomeres of such a system may give rise to complete embryos. 



Hatching — beginning of larval life of amphibian, accomplished by tem- 

 porarily secreted hatching enzymes which aid embryo to escape from 

 its gelatinous capsule. 



Hepatic Sinusoids — maze of dilated and irregular capillaries between loosely 

 packed framework of hepatic tubules. 



Hepatic Veins — veins from liver to heart, originating as anterior portions 

 of vitelline veins of amphibia. 



Hepatic Veins, Portal — remnants of posterior portions of left vitelline vein. 



Hermaphrodite — individual capable of producing both spermatozoa and 

 ova. 



Hermaphrodite, Protandrous — male elements mature prior to female ele- 

 ments in hermaphrodite. 



Hermaphrodite, Protogynous — female elements mature prior to male ele- 

 ments in hermaphrodite. 



Hertwig's Law — nucleus tends to place itself in center of its sphere of ac- 

 tivity; longitudinal axis of mitotic spindle tends to lie in longitudinal 

 axis of yolk-free cytoplasm of cell. 



Heteroagglutinin — agglutinin (fertilizin) of eggs which acts on sperm of 

 different species, substance extractable from egg water which causes 

 irreversible agglutination of foreign species. 



