GLOSSAEY. 317 



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 organised being, whether plant or animal. 



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

 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, 

 &c. 



Paleozoic. — The oldest system of fossiliferous rocks. 



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

 Insects and Crustacea. 



Papilionace^:. — An order of Plants (see Leguminos<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 

 unimpreguated eggs or seeds. 



Pedunculated. — Supported upon a stem or stalk. The peduncu- 

 lated oak has its acorns borne upon a footstool. 



Peloria or Pelorism. — The appearance of regularity of structure in 

 the flowers of plants which normally bear irregular flowers. 



Pelvis. — The bony arch to which the hind limbs of vertebrate 

 animals are articulated. 



Petals. — The leaves of the corolla, or second circle of organs in a 



