522 GLOSSARY 



Di-hy'-brid. The offspring of parents differing in two char- 

 acters. 

 Di-o-nae'-a. An insect-catching plant, the "Venus Fly-trap." 

 Dip'-loid. The full number of chromosomes found in the ferti- 

 lized egg and in all cells derived from this, except the 

 mature germ cells. 

 Dominant character. A character inherited from one parent 

 which develops to the exclusion of a contrasting character 

 of the other parent. 

 Dros-oph'-i-la. A genus of fruit-flies. 



Du'-plex factors or character. A condition where the de- 

 terminers for a character are derived from both parents. 

 E-chi'-no-derms. A phylum of marine animals which includes 



star-fishes and sea-urchins. 

 E-col'-o-gy. The science which deals with the relations of 



organisms to one another and to environment. 

 Ec'-to-derm. The outer layer of cells of an embryo which 



gives rise to epidermis, sense organs and nervous system. 

 Em-bry-og'-e-ny. Early development of an egg leading to 



the formation of an embryo. 

 En'-do-derm. The inner layer of cells of an embryo, which 



gives rise to the digestive cells of the alimentary system. 



Est-do-gen'e-sis (—development from within). The theory 



that the differential causes of development are within the 



germ cells, which are therefore complex. 



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. 



EauATioN-DivisiON. An ordinary nuclear division in which 



each chromosome 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. 



