GENERAL ZOOLOGY 



IMPULSE. See NERVE IMPULSE. 



INCURRENT. AfTording an entrance; leading inward. (.'/. EXCURRENT. 



INDEPENDENT EFFECTOR. A cell responding directly to changes in its environment; 



an elTector that is independent of a reflex arc. 

 INDIRECT CELL DIVISION. See MITOSIS. 



INDIVIDUAL. A physiologically balanced, living unit; an animal or plant. 

 INGESTION. The act of taking food into a place of digestion. Cf. EGESTION. 

 INSTINCT. Reflex action, frequently of a very complex character, dependent on an 



inherited reflex arc. 

 INTEGUMENT. The outer covering of the body; the skin or a derivative of it. 

 INTELLIGENCE. The capacity to profit by experience, based on analysis and as.so- 



ciation of ideas. 

 INTER-. Combining form, meaning "between" or "among." 

 INTERNAL PARASITE. See ENDOPARASITE. 

 INTERNAL SECRETION. .S^^ ENDOCRINE. 

 INTRA-. Combining form, meaning "within." 

 INVAGINATION. I he movement of a group or layer of cells into a cavity. Cf. 



EVAGINATION. 

 INVERTEBRATE. An animal without a vertebral column or backbone. Cf. VERTEBRATE. 

 ISOGAMETES. Gametes of equal size. Cf. ANISOGAMETES. 



ISOGAMY. Fusion of gametes of equal size. Cf. ANISOGAMY and FERTILIZATION. 

 ISOLECITHAL EGG. An egg in which the yolk is not abundant and is almost uni- 



formlv distributed throughout the cvtosomr. Cf. TELOLECITHAL EGG. 



JUVENILE. .\ self-sustaining voung organism that is like the adult of the .species except 

 in size and reproductive maturity. C'f. EMBRYO and LARVA. 



KINETOSOME. The basal body of a cilium; apparently the part of the ciliary mech- 

 anism responsible for initiation of ciliary beating, and in ciliatc protozoans 

 possessing important morphogenetic capacities. 



LACUNA (pL LACUNAE). A cavity or space. 



LAND BRIDGE. ,\ land connection between two other land regions; most often used 



for such a connection that has been submerged. 

 LARVA {pi. LARVAE). A self-su.staining young organism that does not resemble the 



adult. (;f. EMBRYO and JUVENILE. 

 LETHAL. Capable of bringing about death. 

 LEUCOCYTE. A granular white blood cell; a non-pigmented or colorless blood cell. 



Cf. LYMPHOCYTE and ERYTHROCYTE. 

 LIFE CYCLE. The history of an organism or species with reference to its methods of 



reproduction and development. 

 LINEAR. Like a line or thread. 

 LINKAGE. The occurrence of certain characters together in successive generations of 



individuals; a condition arising from the transmission of genes in linkage groups. 

 LINKAGE GROUP. A group of genes that is transmitted from one generation to the 



next as a unit. Cf. GENE STRING. 

 LOCUS {///. LOCI). A place; a localitv; the position occupied by a gene on a gene 



string. 

 LOPHOPHORE. A variously-shaped, tentacle-bearing feeding organ surrounding or 



lying near the mouth, in such forms as Ectoprocta, Brachiopoda, and Phoronidca. 

 LUMEN {pi. LUMINA). A passageway or cavity. 



LUMINESCENCE. The emission of light arising from chemical reactions within cells. 

 LYMPH. A circulating fluid consisting of plasma and white blood cells. 



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