sions connected by a stalk passing nearly through
their centres: also to any part possessing a well-developed
leaf-like or plate-like expansion.

Pergamenous: thin, partly transparent: resembling parchment.

Peri-: round about.

Periopticon: a complex nerve structure back of the basilar membrane
of the eye.

Pericardial: around, or belonging to the heart.

Pericardial cavity: the space between the diaphragm and dorsal body
wall, which contains the heart.

Pericardial cells: specialized cells, which lie along both sides of the
heart, and whose function it is to purify the blood.

Pericardial chamber: is the open space around the heart or dorsal
vessel.

Pericardial diaphragm: a delicate membranous tissue attached
to the ventral surface of the heart and laterally to the body wall
:= dorsal diaphragm wings of the heart.

Peri-intestinal: that part of the body cavity around the alimentary
canal.

Peri-neural: situated around a nerve: the body cavity
immediately surrounding the nervous system.

Periodical: recurring at regular intervals.

Periopticon: third ganglionic swelling of optic tract: see opticon.

Peripheral: referring to the outer margin.

Peripheria: the entire outline of the body.

Periphery: the circumference or outer margin.

Peripneustic: larvae which have the spiracles absent on middle and
posterior thoracic rings, and present on all other body segments.

Peripodal cavities: pouches in the embryo in which the rudiments of
the future legs and wings are developed.

Peripodal membrane: the cell layer surrounding the peripodal cavities.
Peristaltic: that periodic motion of the alimentary canal by means of
which the food is forced toward the anal extremity.

Peristethium: the meso-sternum.

Peristoma -ium: the border of the mouth or oral margin in Diptera;
sometimes used as := epistoma: q.v.

Peristome: a membranous tissue surrounding the mouth parts at
base, and forming the true ventral wall of the head.

Peritoneal: applied to the membrane surrounding the viscera, trachea,
and other internal structures.

Peritracheal: surrounding the trachea.

Peritreme: the corneous selerite surrounding a spiracle.

Peritrophic membrane: a funnel-like extension of the fore-gut,
extending back tube-like, through the chylific ventricle in some
insects.

Perivisceral: the cavity containing the alimentary canal and its
appendages.

Perlate: beaded: bearing relieved, rounded points in series.