690 - Appendix 2 



Holozoic. Kind of nutrition found in typical ani- 

 mals, which ingest organic foods. 



Homeostasis. Tendency of organisms to maintain 

 structural and functional balance in face of en- 

 vironmental change. 



HoMOLF.cn hal EGG. An egg cell with the nonabun- 

 dant yolk uniformly distributed throughout the 

 cytoplasm. 



Homologous chromosomes. The two chromosomes 

 that pair at synapsis. 



Homologous organs. Organs having structural and 

 developmental similarities due to genetic relation- 

 ship, (cf. Analogous organs.) 



Homozygous. Having the two genes of an allelic pair 

 alike, (cf. Heterozygous.) 



Hormone. An internal secretion having some specific 

 effect on metabolism, development, or response of 

 the organism or some particular part of it. 



Hydrolysis. Chemical decomposition of a substance 

 by combination with water. 



Hypocotyl. The part of an embryonic seed plant, 

 below the point of attachment of the cotyledons. 

 (cf. Epicotyl.) 



Independent assortment. The distribution, during 

 meiosis, of the genes of different allelic pairs located 

 in different pairs of homologous chromosomes; the 

 distribution of any such pair of alleles being 

 entirely independent of that of any other such 

 pair. 



Ingestion. Process of taking food into the digestive 

 cavity of an organism. 



Inhibition. The stopping of some activity by a stim- 

 ulus or drug. 



Instinct. A usually invariable complex response in- 

 dependent of any previous experience of the indi- 

 vidual; a complex unconditioned reflex. 



Insulin. An internal secretion of the pancreas essen- 

 tial for the normal metabolism of carbohydrates. 



Intelligence. The ability to learn by experience; 

 i.e., to form conditioned reflexes. 



Intermediate neurons. Neurons connecting sensory 

 with motor neurons. Also called association neurons. 



Internal secretion. Secretion into the blood. Any 

 substance or mixture thus secreted. 



Intestine. The chief portion of the enteron in most 

 animals. 



Invertebrate. Any animal that is not a vertebrate. 



Ion. A part of a molecule, consisting of one or more 

 atoms, with an electric charge. 



Kidneys. The chief excretory organs of vertebrates. 



Kinetic energy. Energy inherent in the motion of a 

 body or of its component particles, (cf. Potential 

 Energy.) 



Kingdom. A primary taxonomic division; all organ- 

 isms are conventionally divided into two kingdoms, 

 plants and animals. 



Krf.iis cycle. A regenerative cycle of oxidation-re- 

 duction and decarboxylation reactions from which 

 cells derive energy (cf. Fig. 8-10) . 



Lactose. Milk sugar, a dissacharide found in the 

 milk of mammals. 



Larva. An active immature animal differing from 

 the adult; e.g., a caterpillar, a tadpole, etc. 



Lecithin. A very common phospholipid, found in 

 many, perhaps all, kinds of cells. 



Leucocites. White blood corpuscles, amoeboid cells 

 of several types, found in most multicellular ani- 

 mals. 



Life cycle. The complete series of forms regularly 

 assumed successively by any particular kind of or- 

 ganism. 



Linkage. The association in heredity of genes lo- 

 cated in the same chromosome. 



Lipids. Organic compounds insoluble in water but 

 soluble in various organic liquids; consisting chiefly 

 of carbon and hydrogen with a small proportion of 

 oxygen and (in some cases) other elements; includ- 

 ing fats, phospholipids, sterols, etc. 



Liver. A large glandular organ of vertebrates with 

 numerous functions, including various special met- 

 abolic processes, storage, and secretion of the bile. 



Locus. A particular position in a chromosome which 

 may be occupied by any gene of a particular allelic 

 series. 



Luciferase. Enzyme essential to the reactions that 

 generate light energy in luminescent organisms. 



Luciferin. Substrate of luciferase. 



Lymph. A fluid derivative of blood plasma usually 

 containing certain white blood corpuscles and rela- 

 tively poor in plasma proteins. 



Lymphatic tissue. A kind of tissue, found in various 

 parts of the body, in which some of the white blood 

 corpuscles are formed. 



Lymphocytes. One kind of white blood corpuscles, 

 formed in the lymphatic tissue. 



Macrocamete. The larger of the two kinds of gam- 

 etes, in organisms that have gametes of two sizes. 



Macrosporancium. A sporangium bearing macro- 

 spores. 



Macrospore. The larger of the two kinds of spores 

 (in plants which have spores of two sizes) , which 

 develops into a female gametophvte. 



Macrosporophyll. A sporophyl bearing macro- 

 sporangia. 



Male. An individual that produces sperm cells but 

 not egg cells. 



Maltose. Malt sugar, a disaccharide produced by in- 

 complete hydrolysis of starch. 



Marrow. A tissue found in the interior of certain 

 bones, in which red blood corpuscles and some 

 kinds of white blood corpuscles are formed. 



Maturation divisions. The two final (mciotic) cell 

 divisions in the formation of the gametes (in ani- 

 mals) or spores (in plants) , in the course of which 

 the chromosome number is reduced from diploid 

 to haploid. 



Medulla. The hindmost portion of the brain, ad- 

 joining the spinal cord. 



Medullar', rays. Strands of tissue connecting pith 

 and cortex, between the fibrovascular bundles. 



Meiosis. The two special divisions by which haploid 

 cells are formed from diploid cells, as in the pro- 

 duction of the gametes of animals and the spores of 

 plants. 



