482 GLOSSARY. 



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 divis- 

 ion 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 be drawn across the eye in Birds and Reptiles, either to mod- 

 erate the effects of a strong light or to sweep particles of dust, etc., 

 from the surface of the eye. 



Neuters. — Imperfectly developed females of certain social insects 

 (such as Ants and Bees), which perform all the labors of the com- 

 munity. Hence they are also called workers. 



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. 

 Operculum. — 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 organized being, whether plant or animal. 

 Orthospermous. — A term applied to those fruits of the Umbelliferqe 



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 have fallen, 



it usually becomes converted into the fruit. 

 Ovigerous. — Egg-bearing. 

 Ovules (of plants). — The seeds in the earliest condition. 



Pachyderms. — A group of Mammalia so called from their thick 



skins, and including the Elephant, Rhinoceros, Hippopotamus, 



etc. 

 Palaeozoic. — The oldest system of fossiliferous rocks. 

 Palpi. — Jointed appendages to some of the organs of the mouth in 



Insects and Crustacea. 

 Papilionace^e. — An order of Plants (seeL,EGUMiNOS,E). — The flowers 



of these plants are called papilionaceous, or butterfly-like, from the 



fancied resemblance of the expanded superior petals to the wings 



of a butterfly. 

 Parasite. —An animal or plant living upon or in, and at the expense 



of, another organism. 

 Parthenogenesis. — The production of living organisms from unim- 



pregnated eggs or seeds. 

 Pedunculated. — Supported u;on a stem or stalk, '"he pedunci* 



lated oak has its acorns borne upon a footstool. 



