726 GLOSSARY. 



Manometer. An instrument for measuring pressure ; made of a U- 



shaped tube containing liquid, commonly mercury. 

 Medullary sheath. A soft, clear sheath around the axis cylinder of 



medullated nerves, which, owing to its refracting power, gives them 



the white appearance. 

 Menstruation. The monthly change in the mucous membrane of the 



uterus which accompanies the discharge of the ovum. 

 Meroblastic. The form of ova in which the yelk does not undergo 



complete segmentation, as that of birds. 

 Mesoblast. The middle of the three layers of the blastoderm from 



which the connective tissues and vascular apparatus of the embryo 



are formed. 

 Metabolism. The intimate chemical changes occurring in the various 



organs and tissues upon which their nutrition and functions depend. 

 Metanephros. The hinder portion of the Wolffian duct which de- 

 velops into the kidney and ureter. 

 Metazoa. A term used to denote all those animals whose ova undergo 



division, in contradistinction to Protozoa. 

 Miorocoocus. . An extremely minute fungus of a round shape. Mi- 



crococci occur in many solutions of decomposing organic matter. 

 Micturition. The act of voiding urine. 

 Molecules. The smallest physical particles of matter that can exist 



in a separate state. They are probably always constituted of two or 



more atoms. 

 Morphology. The science which treats of the forms and structure of 



living beings. 

 Morula. The stage of development of the ovum after segmentation in 



which all the young cells are alike, before the blastoderm is formed. 

 Mlillerian duct. An embryonic structure from which are formed the 



genital passages in the female, viz., Fallopian tubes, uterus, and 



vagina. 



Myograph. An instrument for graphically recording muscle contrac- 

 tion. 

 Myosin. The substance formed by the coagulation of muscle plasma. 



It is one of the globulins. 



Natural nerve currents. The electrical currents passing through 

 an exposed muscle or nerve while in the state of rest. 



Neuroglia. The reticular connective tissue which binds together the 

 elements of the nerve centres. 



Non-polarizable electrodes. Specially constructed electric termi- 

 nals which do not set up secondary currents on application to the 

 moist living tissues. 



