GLOSSARY. 411 



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.) 



MORAINES. The accumulations of fragments of rock brought down by 

 glaciers. 



MORPHOLOGY. The law of form or structure independent of function 



MYSIS-STAOE. 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 distinct genus under the name of Nauplius. 



NEURATION. The arrangement of the veins or nervures in the wings of 

 Insects. 



NEVTERS. 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 Reptiles, 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. 

 OOLITIC. A great series of secondary rocks, so called from the texture of 



some of its members, which appear to be made up of a mass of small 



egg-like calcareous bodies. 

 OPEKCULUM. A calcareous plate employed by many Mollusca to close the 



aperture of their shell. The opercular valves of Cirripedes are those which 



close the aperture of the shell. 



ORBIT. The bony cavity for the reception of the eye. 

 ORGANISM. An organised being, whether plant or animal. 

 ORTHOSPERMOUS. A term applied to those fruits of the Umbellifera which 



have the seed straight. 

 OSCULANT. Forms or groups apparently intermediate between and connecting 



other groups are said to be osculant. 

 OVA. Eggs. 

 OVARIUM or OVARY (in plants). The lower part of the pistil or female organ 



of the flower, containing the ovules or incipient seeds ; by growth after the 



other organs of the flower ha\e fallen, it usually becomes converted into 



the fruit. 



OVIGEROUS. Egg-bearing. 

 OVULES (of plants). The seeds in the earliest condition. 



