GLOSSARY 523 



Fertilization. The union of male and female sex cells. 



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

 as an organ 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 characters of developed organisms (Johannsen). 



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

 viduals and particularly with heredity. 



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

 liarities. "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 develop- 

 ing 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. 



