514 GLOSSARY. 



are generally solid, horny, biting organs. In Birds tlie term is 

 applied to both jaws with their horny coverings. In Quadrupeds 

 the mandible is properly the lower jaw. 



Marsupials. — An order of Mammalia in which the young are born 

 in a very incomplete state of development and carried by the 

 mother, while sucking, in a ventral pouch (marsupium), such as 

 the Kangaroos, Opossums, etc. (see Mammalia). 



Maxilla in Insects. — The second or lower pair of jaws, which are 

 composed of several joints and furnished with peculiar jointed 

 appendages called palpi or feelers. 



Melanism. — The opposite of albinism; an undue development of 

 coloring material in the skin and its appendages, 



Metamorpiiic Rocks. — Sedimentary rocks which have undergone 

 alteration, generally by the action of heat, subsequently to their 

 deposition and consolidation. 



Mollusca. — One of the great divisions of the Animal Kingdom, 

 including those animals which have a soft body, usually furnished 

 with a shell, and in which the nervous ganglia, or centers, pre- 

 sent no definite general arrangement. They are generally 

 known under the denomination of "shell-fish;" the cuttle-fish, 

 and the common snails, whelks, oysters, mussels and cockles, 

 may serve as examples of them. 



Monocotyledons, or Monocotyledonous Plants. — Plants in 

 which the seed sends up only a single seed-leaf (or cotyledon); 

 characterized by the absence of consecutive layers of wood in the 

 stem (endogenous growth), by the veins of the leaves being 

 generally straight, and by the parts of the flowers being gener- 

 ally in multiples of three. {Examples, Grasses, Lilies, Orchids, 

 Palms, etc.) 



Moraines. — The accumulations of fragments of rock brought down 

 by glaciers. 



Morphology. — The law of form or structure independent of func- 

 tion. 



Mysis-stage. — A stage in the development of certain Crustaceans 

 (Prawns), in which they closely resemble the adults of a genus 

 {Mysis) belonging to a slightly lower group. 



Nascent. — Commencing development. 



Natatory. — Adapted for the purpose of swimming. 



Nauplius-form. — The earliest stage in the development of many 

 Crustacea, especially belonging to the lower groups. In this 

 stage the animal has a short body, with indistinct indications of 

 a division into segments, and three pairs of fringed limbs. This 

 form of the common fresh- water Cyclops was described as a dis- 

 tinct genus under the name of Nauplius. 



Neuration. — The arrangement of the veins or nervures in the 

 wings of Insects. 



Nictitating Membrane. — A semi-transparent membrane, which 

 can be drawn across the eye in Birds and Reptiles, either to 

 moderate the effects of a strong light or to sweep particles of 

 dust, etc., from the surface of the eye. 



