236 GLOSSARY 



Kidney: an excretory organ which eliminates nitrogenous wastes from the 

 body. 



Labium: the lower lip of insects. 



LabruHi: the upper lip of insects and of some crustaceans. 



Lamella: a leaf like or plateHke structure. 



Larva: a young animal which has left the egg and is leading a free life, but 



which has not yet completed its development. 

 Lateral: a position to the right or left of the median Hne. 

 Ligament: a tough connecting band. 

 Ligula: the anterior portion of the labium in insects. 

 Lithocyst: a marginal sense organ in certain medusae. 

 Liver: a digestive gland. 

 Lophophore: a circular or horseshoe-shaped ridge bearing tentacles in 



Bryozoa. 

 Lumen: the cavity within a tubular organ. 



Macronucleus: the large nucleus of an infusorian. 



Madreporite: a porous plate through which fluids enter the ambulacral 



system. 

 Malpighian tubules: the kidney of insects and certain other arthropods. 

 Mandible : the anterior pair of mouth parts in arthropods ; the lower jaw 



of vertebrates. 

 Mantle : the integumental fold in mollusks which secretes the shell. 

 Manubrium: the projection of a medusa's body which bears the mouth. 

 Maxillae: the paired mouth parts immediately behind the mandibles in 



arthropods ; the upper jaw of vertebrates. 

 Maxillipeds: the anterior thoracic appendages which assist in mastication 



in crustaceans. 

 Medusa: a medusoid which becomes a free-swimming jellyfish. 

 Medusoid: the sexual generation of a hydromedusan. 

 Megalopa: a larval stage of the crab. 

 Mentum: a division of the labium in insects. 

 Mesentery: a lamella which supports some one of the viscera. 

 Mesothorax: the second thoracic somite in insects. 

 Metamere : one of the serial, homologous body segments, together with its 



appendages, which form the body of an articulate animal. 

 Metamorphosis : the quiescent period in the life of a holometabolic insect 



during which it changes from a larva to an imago. 

 Metasoma: the primitive segmented trunk of an articulate animal. 

 Metastomium: the posterior portion of the prosoma of an annelid. 

 Metathorax: the third thoracic somite in insects. 

 Metazoa: the division of the animal kingdom comprising the many-celled 



animals. 



