490 THE PINEAL ORGAN 



Lepidoptera (Gr. lepis, scale ; pteron, wing) : an order of the Insecta having 

 four wings covered with scales, e.g. butterflies, moths. 



Lepidosiren (Gr. lepis, scale ; surinx, tube) : a genus of the lung-fishes (Dipnoi) 

 of a long pipe-like form, found in South America. 



Lepidosteus (Gr. lepis, scale ; osteon, bone) : genus of ganoid fishes, e.g. 

 gar-pike. 



Lepidurus (Gr. lepis, scale ; oarus, tail) : a crustacean belonging to the subclass 

 Branchiopoda and order Notostraca. It has a well-developed head shield 

 and a tail-like plate between two caudal styles. 



Lingula (L. variant of ligula, spatula or shoe-string) : lamp-shell, a stalked 

 brachiopod in which the two valves of the shell are not joined by a 

 hinge. Existing genera of Lingula appear first in the lower Cambrian 

 rocks, and with other genera of the Brachiopoda, e.g. Cistella, it forms a 

 striking example of persistence of type. See Cistella and Rhynchonella. 



Malacostraca (Gr. malakos, soft ; ostrakon, shell) : a subclass of the Crus- 

 tacea characterized by having a soft shell, e.g. the shrimps and prawns. 



Mantle : the outer covering or pallium which protects the viscera in most 

 of the Mollusca. 



Marsipobranch (Gr. marsipos, pouch ; branchia, gill) : the order of cyclostome 

 fishes, which includes the lampreys and hag-fishes, which is characterized 

 by pouch-like diverticula separated by septa bearing gills. 



Melanoblast (Gr. melas, black ; blastos, bud or germ) : branched pigment 

 cells of the epidermis. They are believed to elaborate pigment granules 

 which pass from them into the epidermal cells. 



Melanophore (Gr. melas, pigment ; phoreo, bear) : a cell bearing pigment 

 granules, also called chromatophore. 



Merostomata (Gr. meros, thigh ; stoma, mouth) : an extinct order of the 

 Crustacea, including the extinct forms Eurypterus and Pterygotus and 

 the living genus Limulus. The appendages situated round the mouth act 

 as jaws, and their free extremities serve as legs or as prehensile organs. 

 The head-shield bears two lateral compound eyes and two ocelli placed 

 near the median line. 



Molluscoida (L. mollis, soft ; mollesco, become soft ; Gr. eidos, likeness) : 

 a subdivision of invertebrates resembling the Mollusca in possessing 

 soft bodies, including the Polyzoa, Brachiopoda, and Phoronida. 



Monostichous (Gr. monos, single ; stichos, layer) : a term applied to an eye 

 consisting of a single layer of cells, e.g. the larval eye of Dytiscus or 

 lateral eyes of Limulus. 



Myriapoda (Gr. murios, numerous, 10,000 ; podes, feet) : a class of the Arthro- 

 poda comprising the centipedes and millipedes. 



Nauplius (L. nauplius, a sea-fish) : the free-swimming larva which results 

 from the hatching of the embryo of certain crustaceans, e.g. Apus. 



Nautilus (Gr. nautilos, sailor) : a genus of the subclass Tetrabranchiata of the 

 class Cephalopoda. It is a primitive type of mollusc the shell of which 

 resembles the extinct Ammonites. 



Nereis : A marine annelid belonging to the subclass Polychaeta. It has two 

 pairs of eyes of a simple ocellar type. 



