338 Glossary 



Ep-i-gen'e-sis (= development from without). The doctrine that the 

 germ is simple and homogeneous and that the differential causes of 

 development are in the environment. 



Equation-Division. An ordinary nuclear division in which each chro- 

 mosome divides equally.- 



Eu-gen'-ics. The system of improving races by good breeding. 



Eu-then'-ics. The system of improving individuals by good environment. 



Ex-o-gas'-tru-la. A gastrula with the endoderm turned out instead of in. 



Factor. A specific germinal cause of a developed character. 



Fertilization. The union of male and female sex cells. 



Fla-gel'-lum. A vibratile thread of protoplasm which serves as an or- 

 gan of locomotion. 



Fluctuations. Variations which are not inherited. 



Fol'-li-cle Cells. Nutritive cells surrounding an ovarian egg. 



Fraternal Twins. Twins produced from different eggs and showing 

 different hereditary characters. 



Functional activity. Use. 



Gam'-ete. The mature male or female sex cell. 



Gang'-li-on. A group of nerve cells. 



Gas'-tro-coel. The digestive cavity of the gastrula. 



Gas'-tru-la. A stage in development following the blastula, in which the 

 embryo consists of an outer (ectoderm) and an inner (endoderm) 

 layer of cells. 



Genes. Factors, units, elements of germ cells which condition the char- 

 acters of developed organisms (Johannsen). 



Ge-net'-ics. The science which deals with the origin of individuals and 

 particularly with heredity. 



Ge'-no-type. The germinal type with all its hereditary peculiarities. "The 

 fundamental hereditary constitution of an organism" (Johannsen). 



Germ-Plasm. The material basis of inheritance. 



Germ-Track. The cell-lineage of the germ cells in a developing animal. 



Germinal Units. Hypothetical parts of germ cells which are supposed 

 to have certain specific functions in development. 



Hae-mo-phil'-i-a. An abnormal condition in which the blood clots 

 slowly. 



Hap'-loid. The reduced number of chromosomes in the gametes. 



Heredity. The appearance in offspring of characters whose differential 

 causes are in the germ cells. 



Heritage. The sum of those characters which are inherited by an 

 individual. 



Het-er-o-zy-go'-sis. Hybridization ; cross-breeding. 



Het-er-o-zy'-gotes. Hybrids resulting from the union of gametes which 

 are hereditarily dissimilar. 



