500 APPENDIX 



Germinal Continuity. The concept of an unbroken stream of germ 

 plasm from the beginning of life, from which each generation is derived. 



Germ Layer. A primary tissue (ectoderm, endoderm, or mesoderm) in 

 the embryo, from which the tissues and organs of the adult animal de- 

 velop. 



Germ Layer Theory. The doctrine that the germ layers are fundamen- 

 tally similar throughout the Metazoa and that homologous structures 

 in various animals are derived during development from the same germ 

 layer. 



Germ Plasm. The physical basis of inheritance. The chromatin (genes) 

 which forms the specific bond of continuity between parent and offspring. 

 Contrasted with soma or somatoplasm. Germ. 



Gill Slits. Paired lateral openings leading from the anterior end of the 

 alimentary canal to the exterior for the exit of the respiratory current 

 of water. Permanent or embryonic characters of Vertebrates Bran- 

 chial clefts. 



Gland. One cell or a group of many epithelial cells which elaborate mate- 

 rials and secrete the product for the use of the organism. 



Glochidium. A bivalved larva of certain fresh-water Mussels, that lives 

 temporarily as a parasite on a Fish. 



Glottis. The opening from the pharynx into the tube (trachea) leading 

 to the lungs. 



Glycogen. So-called animal starch. Sugar is stored as glycogen in liver 

 and muscle cells. 



Golgi Bodies. Formed elements in the cytoplasm; apparently active 

 chemically. 



Gonad. Ovary or testis. 



Gonotheca. Transparent sheath, or exoskeleton, of the reproductive in- 

 dividuals (gonangia) of a Hydroid colony; e.g., Obelia. 



Gray Crescent. Localized organizing substance in Frog's egg. 



Gustatory. Relating to the sense of taste. 



Haploid. The reduced (one-half) number of chromosomes. A complete 

 single set of chromosomes. See Diploid. 



Hemoglobin. Complex chemical compound, in the red blood corpuscles 

 of A ertebratcs, which enters into a loose combination with oxygen, be- 

 coming oxyhemoglobin. Respiratory pigment. 



Hepatic Portal System. Non-oxygenated but food-laden blood from 

 digestive tract passes to the liver by the hepatic portal vein. Oxygenated 

 blood reaches liver by the hepatic artery. Both leave by hepatic vein. 

 Thus there is a double blood supply to liver in all Vertebrates. 



Heredity. The transmission of characters from parent to offspring by 

 the germ cells. 



