316 GLOSSARY. 



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) ; 

 characterised 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 multiples of three. {Examples, Grasses, Lilies, Orchids, 

 Palms, &c.) 



Mobaines. — 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 

 {My sis) belonging to a slightly lower group. 



Nascent. — -Commencing development* 



Natatory. — Adaped 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 iringed limbs. This 

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

 distinct genus under the name of KaupJius. 



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

 wings of Insects. 



Neuters. — Imperfectly developed females of certain social insects 

 (such as Ants and Bees), which perform all the labours of the 

 community. Hence they are also called workers. 



Nictitating Membrane. — A semi-transparent membrane, which 

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

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

 dust, &c, from the surface of the eye. 



Ocelli. — The simple eyes or stemmata of Insects, usually situated 



on the crown of the head between the great compound eyes. 

 (Esophagus. — The gullet. 



