GLOSSARY 601 



morula (m6r' 66 la). An embryo in an early stage when composed of a solid mass of 



cells. 

 mucosa (mu ko' sa). A membrane contatQUig glands by which is formed a mucous 



secretion, 

 mucus (mu'kus). A slimy secretion containing mucin (mu'sin); adj., mucous 



(mu' kiis). 

 Miiller, Johannes P. German physiologist and anatomist; 1801-1858. 

 mutation (mu ta' shtln). A sudden, heritable change in a character possessed by an 



organism due to a change in one or more genes. 

 mutualism (mu' tu al Iz'm). An association of two animals of different species 



which is of advantage to both, 

 myelencephalon (mi 6 I6n s6f' a I6n). The fifth, and most posterior, region of the 



vertebrate brain, including the medulla oblongata, 

 myo (mi' 6). G.; muscle. 



myoneme (mi' 6 nem). A contractile strand in the cytoplasm of a protozoan, 

 mjrria (mlr' la). G.; myriad, literally ten thousand, 

 myx (mlks). G.; sUme. 



Naiad (na' yS,d). The immature stage of an aquatic insect with incomplete meta- 

 morphosis. 



nares (na' rez). The openings into the nasal chamber in vertebrates; the anterior 

 nares open externally and the posterior nares open into the mouth or pharynx. 



nasal (na' zal). Pertaining to the nose. 



natural selection. The process in nature by which the types best fitted for their 

 particular environment survive while those least fitted are eUminated. 



nauplius (no' pll tis). The larva of certain of the Crustacea. 



negative response. A response to a stimulus in which the organism turns or moves 

 away from the stimulus. 



nekton (n6k' t5n). That part of a pelagic aquatic fauna which is independent of the 

 action of winds and waves. 



nemato (ngm' a to). G.; thread. 



nematocyst (n6m' a to sist). One of the stinging bodies found in coelenterates. 



neo- (ne' 6). G.; new, recent. 



neoteny (neSt'enI). The indefinite prolongation of the immature condition of an 

 animal; in tailed amphibians it results in the production of axolotls, and in ter- 

 mites it is shown in the development of reserve females which take the place of 

 lost queens. 



nephridium (ne frid' I tim). An excretory organ found in certain invertebrates. 



nephros (nef r6s). A vertebrate kidney. 



nerve. A collection of nerve fibers inclosed in a sheath. 



nervous. Pertaining to the nervous system or to any of its functions. 



nervous impulse. The effect of stimulation transmitted along a nerve fiber. 



nervure (nur' vur). A stiffening riblike structure in the wing of an insect. 



neural. Pertaining to a nerve or to the nervous system. 



neurilemma (nu rl Igm' a). The delicate membrane covering a nerve fiber. 



neuron (nu' ron). A nerve cell, including the cell body and all the branches, or 

 fibers. 



nid (nid). L.; nest. 



noct (nokt). L.; night. 



nomenclature (no' mgn kla tyiir). A system of naming objects or concepts. 



noto (no' to). G.; the back. 



notochord (no' to kord). A rod of cells, derived from the entoderm, in the chordates 

 lying in the median line below the spinal cord; it disappears as the vertebral 

 column is developed; also called chorda dorsalis, or simply chorda. 



