412 GLOSSARY. 



PACHYDERMS. A group of Mammalia, so called from their thick skins, and 



including the Elephant, Rhinoceros, Hippopotamus, &c. 

 PALAEOZOIC. The oldest system of fossiliferous rocks. 

 PALPI. Jointed appendages to some of the organs of the mouth in Insects 



and Crustacea. 

 PAPiLiONACEjE. An order of Plants (see LEGt'Mrxos.). 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 unimpregnated 



eggs or seeds. 

 PEDUNCULATED. Supported upon a stem or stalk. The pedunculated oak 



has ite 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 flower. 



They are usually of delicate texture and brightly coloured. 

 PHYLLODIXEOUS. Having flattened, leaf-like twigs or leafstalks instead of 



true leaves. 

 PIGMENT. The colouring material produced generally in the superficial parts 



of animals. The cells secreting it are called pigment-cells. 

 PINNATE. Bearing leaflets on each side of a central stalk. 

 PISTILS. The female organs of a flower, which occupy a position in the 



centre of the other floral organs. The pistil is generally divisible into the 



ovary or germen, the style and the stigma. 



PLACENTALIA, PLACENTATA, or Placental Mammals. See MAMMALIA. 

 PLANTIGRADES. Quadrupeds which walk upon the whole sole of the foot, 



like the Bears. 



PLASTIC. Readily capable of change. 



PLEISTOCENE PERIOD. The latest portion of the Tertiary epoch. 

 PLUMULE (in plants). The minute bud between the seed-leaves of newly- 

 germinated plants. 

 PLUTONIC ROCKS. Rocks supposed to have been produced by igneous action 



in the depths of the earth. 

 POLLEN. The male element in flowering plants ; usually a fine dust produced 



by the anthers, which, by contact with the stigma, effects the fecundation of 



the seeds. This impregnation is brought about by means of tubes (pollen. 



tubes) which issue from the pollen-grains adhering to the stigma, and 



penetrate through the tissues until they reach the ovary. 

 POLYANDROUS (flowers). Flowers having many stamens. " 

 POLYGAMOUS PLANTS. Plants in which some flowers are unisexual and others 



hermaphrodite. The unisexual (male and female) flowers, may be on the 



same or on different plants. 

 POLYMORPHIC. Presenting many forms. 

 POLYZOARY. The common structure formed by the cells of the Polyzoa, 



such as the well-known Sea-mats. 

 PREHENSILE. Capable of grasping. 

 PREPOTENT. Having a superiority of power. 

 PRIMARIES. The feathers forming the tip of the wing of a bird, and inserted 



upon that part which represents the hand of man. 

 PROCESSES. Projecting portions of bones, usually for the attachment of 



muscles, ligaments, &c. 

 PROPOLIS. A resinous material collected by the Hive-Bees from the opening 



buds of various trees. 



