392 PRINCIPLES OF ANIMAL BIOLOGY 



Neuromuscular (nu' ro mus' ku ler). Combining the functions of contraction and the 

 transmission of impulses. 



Neuron {nu' rone). A nerve cell. 



Nitella (ni teV la). A genus of aquatic plants. 



Nomenclature (no' men Ma' ture). A system of naming; terminology. 



Nostril (nos' tril). One of the external openings of the nasal chamber. 



Notochord {no' to kord). A cylindrical rod of cells beneath the nervous system of an 



embryo (adult of some animals). It is the fore-runner of the spinal column of the 



vertebrate animals. 



Notophthalmus {no' tof thai' mus) . A genus of salamanders. 



Nototrema {no' to tre' ma). A genus of frogs. 



Nuchal plate {nu' kal). In turtles, the median plate of the carapace at the anterior 

 end. 



Nuclear membrane {nu' kle ar mem' hrane). A thin film of protoplasm surrounding 

 the nucleus of a cell. 



Nuclear sap {nu' kle ar sap'). The Uquid forming the bulk of the nucleus of a cell. 

 Nuclein {nu' kle in). One of a number of protein compounds involving nucleic acid, 

 found in abundance in cell nuclei. 



Nucleolus {nu kle' o lus). A small, usually rounded body found in the nuclei of many 

 cells, which is of different chemical composition from the rest of the nucleus. Its 

 function is uncertain. 



Nucleus {nu' kle us). A highly refractive, deeply staining body of specialized proto- 

 plasm found within nearly all cells. 



Obelia (o be' li a). A genus of hydroids, or colonial Hydra-like animals of the phylum 



Coelenterata. 

 Octopus {ok' to pus). A genus of devilfishes (moUusks) having eight arms. 

 Oenothera (e' no the' ra). A genus of plants to which the evening primroses belong. 

 Oken, Lorenz {o' ken). German naturaUst and transcendentalist philospher, 1779- 



1851. 

 Oleic (o le' ik) . A fatty acid entering into the composition of olive oil. 

 Olfactory {olfak' to ri). Pertaining to the sense of smell. 



Oligocene {of i go seen). Of early Tertiary time, between Eocene and Miocene. 

 Oligochaeta {oV i go ke' ta) . A subclass of Chsetopoda (Annelida), including chiefly 



terrestrial and freshwater worms with relatively few setse which do not rest on 



fleshy outgrowths, but project directly from the body wall. The earthworm is an 



example. 

 Onychophora {on' i kof o ra). A class of primitive Arthropoda having tracheae and 



one pair of antennae. Peripatus is an example. 

 Oocyte {o' o site). A female germ cell subsequent to the initiation of maturation and 



prior to the second maturation division. An oocyte is designated primary during 



the growth period and prior to the first division; secondary after the first 



division and before the second. 

 Oogenesis (o' ojen' e sis). The maturation of female germ cells. 

 Oogonium (o' o go' ni um). One of the early germ cells of a female animal, prior to the 



beginning of maturation. 

 Oosperm {o' o sperm). A fertilized ovum; a term usually applied to plants rather than 



animals. 



