698 GLOSSARY 



Interray^ One of the divisions of the radiate body of echinoderms. 

 Intestine. The division of the digestive tract in which absorption goes on. 

 Introvert. The anterior part of a sipunculid, which can be invaginated. 



Keher's organ. An excretory organ in pelecypods. 

 Kidney. An excretory organ. 



Labium. The under lip of many arthropods. 



Lamella. A leaf- or plate-like 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 line. 



Lateral teeth. In the radula of mollusks the teeth on each side of the cen- 

 trals; in pelecypods the hinge-teeth either anterior or posterior to the 

 cardinals. 



Ligament. The elastic band joining the two valves of a pelecypod's shell. 



Lip. The margin of the aperture of a snail shell. 



Lithocyst^ A marginal sense-organ in campanularian medusae. 



Liver. A digestive gland. 



Lophophore. A circular or horseshoe-shaped ridge bearing tentacles in Bryozoa, 

 Brachiopoda and Phoronidea. 



Lorica. The shell enclosing the body in many rotifers. 



Lumen. The cavity within a tubular organ. 



Lunule. A depressed area in front of the umbo in certain pelecypods. 



Lycophore. The ten-hooked embryo of the Cestodaria. 



Macronucleus. The large nucleus of an infusorian. 



Madreporite. The porous plate through which fluids enter the ambulacral 



system. 

 MalpigJiian tubes. The kidney of insects and many arachnids. 

 Mammary organ.^ An elevation in the vestibule of certain entoproct bryozoans 



which nourishes the embryos. 

 Mandible. The anterior pair of mouth-parts in arthropods. 

 Mantle. The integumental fold in mollusks and brachiopods which secretes the 



shell; the body-wall of ascidians beneath the tunic. 

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

 Marginal teeth. In the radula of mollusks the teeth at the side of the laterals. 

 Mastax. The muscular pharynx of a rotifer. 



Maxilla. The paired mouth-parts immediately behind the mandibles in arthro- 

 pods. 

 Maxillipeds. The anterior thoracic appendages in crustaceans and centipeds. 

 Medusa. A free-swimming jelly-fish. 



Medusoid. The sexual generation of the Hydromedusae and Scyphomedusae. 

 Megascleres. The larger spicules in sponges which form the principal skeletal 



supjjort. 

 Mesentery. A lamella which supports some one of the viscera; in Scyphozoa 



and Anthozoa a lamella extending from the body-wall into the gastrovas- 



cular space. 

 Mesoglca. The middle tissue between the ectoderm and entoderm in Coelen- 



terata. 

 Metacnemes. The secondary mesenteries of AnthoJroa. 

 Metamere. One of tlie serial, lioniologous body-segments, together with its 



appendages, which form the body of an articulate animal. 

 Mctapodium. The hinder part of tlie molluscan foot. 

 Metasoma. The primitive segmented trunk of an articulate animal. 

 Mctastomium. The posterior portion of the head of an annelid. 



