GLOSSARY 915 



Morphology (morfol'o ji), the science that treats of the form and structure 



of the lindies of animals. 

 Morula (mor'ula), a type of blastula characterized by the absence of a seg- 

 mentation cavity. 

 Mucosa (muko'sa), a cellular membrane lining such cavities as those of the 



digestive tract. 

 Mucus (mu'kus), a viscous secretion which contains mucin (mu'sin). Mucous 



IS the adjective form. 

 Mutation (mtita'shun), a heritable change in an organism due to changes in 



one or more genes of germ cells. 

 Mutualism (mii'tualiz'm), animals of different species associating together for 



the mutual advantage of each. 

 Myelencephalon (mi e len sef'alon), the fifth or most posterior division of the 



vertebrate brain; the medulla oblongata of the adult. 

 Myelin (mi'elin), fatty substance surrounding the axone in medullated nerve. 

 Myoneme (mi'6nem), contractile fiber or strand in the cytoplasm of certain 



protozoans. 

 Myotomes (mi'6 toms), segmental divisions of the muscles. 

 Myxnoidea (mik si noi' dea), subclass of Cyclostomes including hags. The 



name means slime and form. 



Nares (na'rez), the openings into the nasal chambers in vertebrate animals. 



Nauplius (no'pliiis), a larval stage of certain Crustacea. 



Nekton (nek'ton), the pelagic aquatic animals which are independent of the 



effect of wind and waves. 

 Nematocysts (nem'a to sists), stinging bodies found in the tentacles of certain 



coelenterates. 

 Nematode (nem'a tod), a roundworm belonging to class Nematoda of phylum 



Nemathelminthes. 

 Neoteny (neot'eni), the indefinite persistence of the immature condition of 



an animal. 

 Nephridium (nefrid'iiim), a form of excretory organ, as found in the earth- 

 worm. 

 Neplirostome (nef'ro stom), the funnel-shaped aperture at the medial end of a 



nephridium. 

 Neural (nii'ral), pertaining to the nervous system or to a nerve. 

 Neurilemma (nurilem'a), the membranous outer coat of a nerve fiber. 

 Neuroid transmission (nu'roid), primitive transmission of impulses from cell 



to cell. 

 Neuron (nu'r5n), a nerve cell together with its processes. 

 Nidamental gland (nid'ament al), one of the reproductive organs of the female 



squid. 

 Notochord (no'tokord), a flexible rod extending anterior to posterior in the 



longitudinal axis of the body dorsal to the digestive tube and ventral 



to the nerve cord in chordates. 

 Nocturnal (nok tur'nal), reference to night. Contrasted to diurnal which per- 

 tains to daytime. 

 Nodes of Ranvier (ranvya'), constrictions in medullated nerve where the 



myelin sheath is interrupted. 

 Nomenclature (no'men kla tur), a system of naming objects or ideas. 

 Nondisjunction (non dis jungk'shiin), the failure of homologous chromosomes 



to separate after synapsis and both go to one daughter cell with none 



to the other. 

 Nucleolus (nu kle'6 liis) (Plasmosome), a body within the nucleus containing 



material that is not chromatin. 



