163 Per 



Pericardium. — The irregular chamber which is 

 bounded above by the upper body-wall, and its 

 muscles, and below by the pericardial diaphragm, 

 and in which the " heart " lies. (Gr, peri, and 

 hardia, the heart.) 



Periopticon. — An object of retinal structure, con- 

 sisting of a series of rod-like pigmented nerve- 

 cells surrounded by small " chaplet-cells " with 

 a large nucleus, and connecting the nerve-fibres 

 which pass out through the perforated mem- 

 brane to the retinulse surrounding the eye-rods. 

 (Gr. peri, and optikos, pertaining to the sight.) 



Peripheria. — The contour ; surface. (Gr. peri, 

 and phero, to bear.) 



Peripneustic. — A term given to one of the inter- 

 mediate types between the holopneustic and 

 apneustic tracheal systems. When the pro- 

 thoracic and abdominal spiracles are open, while 

 the mesothoracic pair are closed or atrophied. 

 (Larvae of Coleoptera, Lepidoptera, Hymen- 

 optera, Neuroptera, Mecoptera, and Trichop- 

 tera.) (Gr. peri, and from pnemna air.) 



Peristaethium. — The Peristethium. That portion 

 of the postpectus anterior to the insertion of the 

 legs ; it extends laterally to the scapulse, and is 

 generally connected to the pectus by a mem- 

 brane (Say.) 



Peristetliium. The anterior central part of the 

 medipectus, lying in front of the sockets of the 

 intermediate legs. (Gr. peri, and stethos, the 

 breast.) 



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