Appendix 845 



Negative tropism (tro' pizm) (Gr. trope, turning), tendency to move away from 



a stimulus. 

 Nemathelminthes (ne math el -min' thcz) (Gr. nema, round; helmins, worm), 



roundworms. 

 Nematocyst (nem' a to sist) (Gr. yiema, thread; kystis, sac), permanent, stinging 



thread thrust from a saclike cell as in Hydra. 

 Nematode (nem' a tod), class of roundworms. 

 Neoplasm (ne'oplazm) (Gr. neos, new; plasma, formation), newly added tissue, 



generally pathologic. 

 Neoteny (pedogenesis) (ne-ot'oni) (Gr. neos, new; teinein, to stretch), re- 

 tention of larval traits throughout life, even being sexually mature in this 



larval condition. 

 Nephritic (ne -frit' ik) (Gr. nephros, kidney), pertaining to the kidney. 

 Nephridium (ne -frid' i um) (Gr. nephros, kidney), tubular excretory organ of 



lower animals as earthworms. 

 Nephrostome (nef'rostom) (Gr. nephros, kidney; stoma, opening), ciliated open- 

 ing of inner end of a nephridium. 

 Nerve (L. nervus, sinew), group of nerve fibers, end to end and side by side, 



held together by special connective tissue called neuroglia. 

 Neural groove, tube, see Medullary groove, etc. 

 Neurilemma (nu ri -lem' a) (Gr. neuron, nerve; lemma, covering), membranous 



covering of nerve. 

 Neuroblast (nu'ro blast) (Gr. neuron, nerve; blastos, origin), cell which embryo- 



logically gives rise to nerve cells. 

 Neuroglia (nu-rog'lia) (Gr. neuron, nerve; glia, glue), special tissue to bind 



and support nerve cells and fibers. 

 Neuromuscular, combining nervous and muscular functions. 

 Neuron (nu' ron) (Gr. neuron, nerve), unit of the nervous system composed of 



dendrite, cyton, and axon. 

 Nissl's granules (Nis' 1) (after Nissl), present in nerve cell cytoplasm and asso- 

 ciated with its activity. 

 Nitrification (ni tri fi -ka' shun), preparation of nitrogenous materials for use by 



organisms. 

 Nitrifying bacteria, those capable of changing ammonia into nitrites or nitrites 



into usable nitrates. 

 Nitrogen-fixing bacteria, those capable of combining free nitrogen of the air 



with oxygen, either in the nodules of the roots of leguminous plants (such 



as clovers, peas, alfalfa, etc.) or by other species of bacteria that live 



freely in the soil. 

 Nodes of Ranvier (ran-vya'), places on a nerve fiber where the membranous 



covering (medullary sheath) is interrupted. 

 Nomenclature (no' men kla-tur) (Gr. nomen, name), system of naming objects 



or organisms. 

 Nondisjunction (non dis jungk' shun), failure of homologous chromosomes to 



separate after synapsis, both going to one cell. 

 Nonelectrolyte (non e -lek' tro lite), a substance such as sugar or alcohol which, 



in solution, cannot be ionized and hence cannot conduct electric currents. 

 Notochord (no' to kord) (Gr. notos, back; chorde, string), rodlike structure in 



the dorsal (back) side which is the forerunner of backbone. 



