GLOSSARY 461 



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). 



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 color- 

 ing material in the skin and its appendages. 



Metamorphic Rocks. — Sedimentary rocks which have undergone al- 

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

 deposition and consoHdation. 



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) ; charac- 

 terized 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 generally in mul- 

 tiples of three. (Examples, Grasses, LiHes, 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. 



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 divi- 

 sion into segments, and three pairs of fringed limbs. This form of 

 the common fresh-water Cyclops was described as a distinct 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 



