518 GLOSSARY 



Linin (li'nin), the delicate threadlike structure which supports the chromatin 

 granules in the nucleus. 



Linkage (lingk'ij), the constant association of particular genes in certain 

 chromosomes. 



Lipase (li'pas), a fat-splitting enzyme. 



Lipin (li'pin), fatty substance. 



Lipoid (lip'oid), fatlike substance. 



Lophophore (lo'fofor), a disc which surrounds the mouth and bears the tenta- 

 cles of the Bryozoa. 



Lumbar (lum'ber), pertaining to the region usually known as the small of the 

 back. 



Lumen (lu'men), internal cavity of a tubular duct, gland, vessel, etc. 



Luminescence (lu mi nes'ens), the emission of light from the body. 



Lymph (limf), the blood plasma and white corpuscles in the lymph spaces about 

 the tissues. 



Lymphatic (limfat'ik), a vessel which carries lymph. In general, pertaining 

 to lymph. 



Macronucleus (mak ro nu'kle us), the large nucleus of certain protozoans sup- 

 posed to control vegetative functions. 



Madreporite (mad're p6 rit), the strainerlike external aperture of the water- 

 vascular system of echinoderms. 



Malpighian (malpig'ian) body, a structure in the cortex of the kidney, com- 

 posed of a glomerulus and Bowman's capsule which serves to take urine 

 from the blood. 



Mantle (man't'l), a fold of the body wall which partially envelops the body; 

 present in most mollusks and here secretes a shell. 



Marsupial (mar su'pi al), having a pouch for carrying the young. 



Marsupium (mar su'pi um), an external pouch used in carrying the young, as 

 in the kangaroo or opossum. 



Matrix (ma'triks), the mother substance, such as that which encloses anything; 

 the intercellular material of cartilage or other sustentative tissue. 



Maturation (mat u ra'shun), the series of changes occurring in the development 

 of germ cells before fertilization, including a reduction in the number of 

 chromosomes in the cells. 



Maxilla (maksil'a), the major bone of the upper jaw of vertebrates or the 

 accessory mouth part just back of the mandibles in many invertebrates. 



Medulla (medul'a), posterior portion of the vertebrate brain; also the median 

 area of many organs. 



Medullary (med'ii ler i), pertaining to the medulla. 



MeduUated (med'ii lat ed), term used in reference to a nerve fiber which pos- 

 sesses a fatty or myelin sheath. 



Medusa (medii'sa), a free-swimming individual coelenterate, such as a jelly- 

 fish. 



Meiosis (mi 6'sis), the reduction division in maturation of germ cells. 



Meridional (me rid'i o nal), a condition in which planes extend from pole to 

 pole of a spherical body. 



Meroblastic (mer 6 blas'tik), having the type of egg structure in which cleavage 

 is only partial, owing to the accumulation of yolk in the egg. 



Mesencephalon (mes en sef'a Ion), the third region of the vertebrate brain, com- 

 monly called midbrain. 



Mesenchyme (mes'eng kim) (Parenchyma), undifferentiated mesoderm composed 

 of large cells. 



Mesoderm (mes'odurm), the middle germ layer and its later derivatives. 



Mesoglea (mesogle'a), a jellylike substance found in Coelenterata between the 

 ectoderm and endoderm. 



Mesonephros Cmes 6 nef'ros), the vertebrate kidney of forms from lamprey to 

 amphibians inclusive. 



Mesorchium (me sor'ki um), the mesentery or membrane supporting a testis. 



