GLOSSARY. 481 



MalacostrAcA. — The higher division of the Crustacea, including the 

 ordinary Crabs, Lobsters, Shrimps, etc., together with the Wood- 

 lice and Sand-hoppers. 



Mammalia. — The highest class of animals, including the ordinary 

 hairy quadrupeds, the Whales and Man, and characterized by the 

 production of living young which are nourished after birth by milk 

 from the teats (Mamma*, Mammary glands) of the mother. A 

 striking difference in embryonic development has led to the divis- 

 ion of this class into two great groups; in one of these, when the 

 embryo has attained a certain stage, a vascular connection, called 

 the placenta, is formed between the embryo and the mother; in 

 the other this is wanting, and the young are produced in a very 

 incomplete state. The former, including the greater part of the 

 class, are called Placental mammals ; the latter, or Aplacental 

 mammals, include the Marsupials and Monotremes (Ornitho- 

 rhynchus). 



Mammifekous. — Having mammae or teats (see Mammalia). 



Mandibles in Insects. — The first or uppermost pair of jaws, which 

 are generally solid, horny, biting organs. In Birds the 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 Kan- 

 garoos, Opossums, etc. (see Mammalia). 



Maxillae 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. 



Metamokphic 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, in- 

 cluding those animals which have a soft body, usually furnished 

 with a shell, and in which the nervous ganglia, or centres, present 

 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 gener- 

 ally straight, and by the parts of the flowers being generally in mul- 

 tiples 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 function. 



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. 



