502 APPENDIX 



Immunity. Resistance of the body to infection by disease-producing 

 organisms. Exemption from disease. 



Independent Assortment. Members of different pairs of genes, located 

 in different pairs of chromosomes, are distributed independently. 



Infundibulum. A funnel-like outgrowth from the ventral wall of the 

 diencephalon. , See Pituitary Gland. 



Intercellular Digestion. Digestion by the secretion of enzymes into a 

 digestive cavity; e.g., in Earthworm and Man. See Intracellular Diges- 

 tion. 



Internal Receptors. Sense organs within the body. See External Re- 

 ceptors. 



Internal Secretion. See Hormone and Ductless Gland. 



Intestine. Portion of the alimentary canal. In higher forms, portion 

 from pyloric end of stomach to cloaca or anus. Usually divided into 

 small and large intestine. 



Intracellular Digestion. Digestion of food within the cell itself; e.g., 

 in Paramecium and to some extent in the endoderm cells of Hydra. See 

 Intercellular Digestion. 



Invagination. Sinking or growing in of a portion of the surface of a hol- 

 low body; e.g., during transformation of blastula into gastrula. 



Invertebrate. Animal without a notochord or a vertebral column. 



Irritability. The power of responding to stimuli, exhibited by all proto- 

 plasm. 



Karyolymph. The more fluid material of the nucleus in contrast with the 



linin and chromatin. 

 Katabolism. The destructive phase of metabolism. See Anabolism. 

 Kinetic Energy. Energy possessed by virtue of motion; e.g., union of 



C with O2 transforms chemical potential energy into kinetic energy, 



i.e., heat, etc. See Potential Energy. 



Lacteals. Lymphatic vessels of the small intestine. 



Lamarckism. Essentially the doctrine of the inheritance of modifications, 



or acquired characters, as a factor in evolution. 

 Larva. An immature stage in the life history of certain animals, usually 



active and differing widely in appearance from the adult; e.g., cater- 

 pillar of Rutterfly, tadpole of Frog. 

 Linin. Non-stainable portion of the nuclear reticulum, probably closely 



related chemically to chromatin. 

 Linkage. The inheritance together of characters represented by genes in 



the same chromosome. Independent assortment does not occur. 

 Lipids. Fatty substances including the true fats and such compounds as 



cholesterol (C27H45OH) and the lecithins containing also phosphorus and 



nitrogen. See Fats. 



