370 ANIMAL BIOLOGY. 



Lamina. A thin film or plate. Lamina perpendicularis, part of the eth- 

 moid bone ; Lamina spiralis in the organ of hearing ; Lamina termin- 

 alis, the front wall of the brain. Laminae, dorsales, the ridges which 

 bound the neural or medullary groove. 



Larva. The freed embryo of certain organisms, such as insects. 



Ligament. (1) A fibrous band of connective tissue by which the bones 

 are connected at the joints or articular surfaces ; (2) a fibrous elastic 

 band where the shell of the mussel is not calcified. 



Liver. A large secreting gland of the vertebrate. The term liver is often 

 applied to the digestive gland of the invertebrate. Since this has 

 often pancreatic properties, it is sometimes called the hepato-pancreas. 



Lobe. A part of an organ separately folded off. There are lobes of the 

 brain, liver, lungs, and many other organs ; a lobule is a little lobe. 



Lumen. The central cavity of a fine tube, duct, or vessel. 



Manubrium. (1) A process of the sternum. (2) A process of the hammer 

 bone or malleus of the ear. (3) The clapper of the bell in a medusa. 



Maxilla. (1) A jaw-bone in the vertebrate skull. (2) An appendage in 

 the crayfish and the cockroach. 



Medulla. (1) The pith-like substance in the axis of a feather. (2) Medulla 

 oblongata, the hinder part of the brain. (3) Medullary folds, groove, 

 and tube, the first indications of the central nervous system, now 

 often termed the neural folds, tube, etc. (4) The internal striated 

 part of the kidney, as opposed to the outer dotted cortical part. (5) 

 Medullary cords, strands of lymphatic tissue in a lymphatic gland. 



Membrane. A thin sheet of tissue, forming an investment or a distinct 

 layer. 



Meroblastic. See Holoblastic. 



Mesenteron. See Archenteron. 



Mesentery. A fold of peritoneal membrane by which the alimentary 

 canal is suspended in the body-cavity or coelom. 



Mesostates. See Metabolism. 



Metabolism. A term applied to the chemical changes associated with 

 living cells. Metabolism may result in the formation of more complex 

 compounds (anabolism), or of less complex compounds (katabolism}. 

 Anabolism is associated with the storage of energy in the tissues ; 

 katabolism with the activities of the organism. Intermediate com- 

 pounds are called mesostates ; as terms of a katabolic process, kata- 

 states ; of an anabolic process, anaslates. 



Metameres. Serially homologous divisions of an organism. 



Metamorphosis. The series of changes taking place during the free life of 

 the organism by which it passes from the embryonic to the adult state. 

 When the changes take place before birth or hatching the term trans- 

 formation is used. 



Metazoa. Organisms composed of many cells, in which a physiological 



