GLOSSARY 367 



the digestive enzymes, which accelerate the hydrolysis of 

 starches, fats, and proteins. 

 Epigenesis: Development of the embryo by differentiation 

 of previously undifferentiated protoplasm. 



Fats: Esters of the higher fatty or organic acids (such as 

 stearic, palmitic, and oleic) esterified with the trihydric 

 alcohol glycerine (glycerol). 



Gamete: A reproductive cell specialized for syngamy, i.e., 

 for union with a complementary germ cell, their union 

 giving rise to a synthetic cell known as a zygote. 



Ganglion: An aggregate of nerve-cells consisting mainly of 

 neural cell-bodies together with supporting cells. 



Ganoids: Fishes covered with enameled bony scales, and 

 now, for the most part, extinct. 



Gene: A factor or infinitesimal element in a nuclear thread 

 or chromosome, the latter being a linear aggregate of 

 such factors, each having definite specificity and mani- 

 festing itself in the external character which develops 

 from it. 



Genotype: The total assemblage of germinal factors trans- 

 mitted by a given species of organism, that is, the complete 

 complex of genes synthesized in the zygote and perpetu- 

 ated by equation-divisions in the somatic cells. Hence 

 the basic germinal or hereditary constitution of an 

 organism or group of organisms. 



Germ Cells: Cells specialized for reproduction as contrasted 

 with other vital functions, e.g., spores and gametes. 



Germ-plasm: The material basis of inheritance. 



Glacial Epoch: After the close of the Tertiary period, 

 Europe and North America are said to have been cov- 

 ered with vast ice sheets known as continental glaciers 

 (the result of great climatic changes in the Northern hemi- 

 sphere) . As the weather varied these ice sheets advanced 

 and retreated, the retreats corresponding to the so-called 

 Interglacial intervals. Four Glacial and three Inter- 

 glacial stages are distinguished, and it was during the 

 Second and Third of these Interglacial stages that Palaeo- 

 lithic Man is alleged to have entered Europe. 



