472 GLOSSARY. 



PLACOID, a term applied to a group of fishes having scales 

 of a broad flat form. Gr. plax, a broad flat surface, and 

 eidos, form. 



PLAGIO'STOMI, the order of cartilaginous fishes which includes 

 the Sharks and Bays. Gr. plagios, slanting, and stoma, 

 a mouth. 

 PLASTRON, a term applied to the shell or plate that covers the 



lower surface of the body of the Tortoise. 

 PLECTOGNATHI, an order of osseous fishes in which the jaws are 

 united, as in the Globe-fish and Trunk-fish. Gr. plektos, 

 plaited, and gnathos, the jaws. 

 POLLEN, the farina or fine dust contained in the anthers of 



flowers. 



POLYGA'STRICA, one of the great divisions of the Infusory ani- 

 malcules, characterised by the possession of a number of 

 sacs or stomachs for the reception of food. Gr. polys, many, 

 gaster, the belly. 

 POLYGONAL, having many angles and sides. Gr. polys, many, 



and gonia, an angle. 



POLYPES, rayed animals which were formerly supposed to par- 

 take of the nature of both plants and animals. The tenta- 

 cula when expanded bear some resemblance to the arms of 

 Cuttle-fishes, known to the ancients as Polypi; hence the 

 origin of the name. 



POLY'PIDOM, the horny sheath with which the soft body of the 

 Polypes is invested. Lat. polypus, a polyp, and domus, a 

 house. 



PREHENSILE, having the power of seizing.") Lat. prehendere, to 



PREHENSION, the act of seizing. ) take, seize, or catch. 



PRIMARIES, the terminal feathers of the wings of birds. They 



grow on the parts which correspond to the bones of our 



hands. 



PRISMATIC COLOURS, the beautiful rainbow tints produced by 



the refraction of a ray of light by means of a prism. 

 PRIME'VAL, belonging to the first or earliest ages. Lat. primum 



cevum, the first time. 

 PROBOSCIS, a fleshy prolongation of the snout, as seen in the 



Tapir, or in the trunk of the Elephant. 



PROCESS, an anatomical term meaning a projecting portion. 

 In this sense, it has a different signification from the same 

 word as used in arts and manufactures. 



PROPAGATION, the continuance of species; the generating of 

 young individuals from the parent stock. Lat. propagare, 

 to multiply or increase. 



PRO'TOTYPE, the first or original form or model. Gr. protos 

 first, typos, impression. In Zoology, the term is applied to 

 a species in which the characteristics of the group to which 

 it belongs are well developed. 



PTERO'PODA, a class of mollusca which have two membranous 

 expansions like fins or wings, and are hence spoken of as 

 " wing-footed." Gr. pteron, a wing, and pous, a foot. 

 PULMONARY, pertaining to the lungs. Lat. pulmo, a lung. 



