PER- 



234 



PER- 



or microspore-coating of certain 

 Pteridophytes (hot.). 



periodicity (pe'riodis'itT) n. [Gk.peri, 

 round ; odos, a way.] The fulfil- 

 ment of functions at regular periods 

 or intervals ; rhythm (&/.). 



perioesophageal (per'ie'sofaje'al) a. 

 [Gk.peri, round ; oisophagos, gullet.] 

 Surrounding the oesophagus ; appl. 

 a nerve ring (zoo/.). 



periosteum (peYlos'teum) n. [Gk. 

 pert, round ; osteon, bone.] The 

 connective membranous tissue in- 

 vesting the surface of bones (anat.). 



periostracum (per'los'trakum) n. [Gk. 

 peri, round ; ostrakon, shell.] The 

 chitinous external layer of most 

 Mollusc shells (zoo/.). 



periotic (peViot'ik) n. [Gk. peri, 

 round ; ous, ear.] A cranial bone 

 enclosing parts of the membranous 

 labyrinth of the internal ear (anat.). 



peripetalous (per'ipet'alus) a. [Gk. 

 peri, round ; petalon, a leaf.] Sur- 

 rounding petals or a petaloid struc- 

 ture (oof.). 



peripharyngeal (peYifarin'jeal) a. 

 [Gk.peri, round ; pharyngx, gullet.] 

 Encircling or surrounding the 

 pharynx ; appl. the cilia of Ascidi- 

 ans (zoo/.). 



peripheral (pgrlfgral) a. [Gk. peri, 

 round ; pherein, to bear.] Distant 

 from the centre ; near the circum- 

 ference ; appl. end-organs of nerves, 

 nervous system (anal.). 



peripherical (per'ifeYikal) a. [Gk. 

 peri, round ; pherein, to bear.] 

 Appl. an embryo more or less 

 completely surrounding the endo- 

 sperm in the seed (dot.). 



periphery (pe'rif'e'ri) n. [Gk. peri, 

 round ; pherein, to bear.] The 

 boundary outline of a surface or 

 part. 



periphysis (pgrlf'isis) n. [Gk. peri, 

 round ; physis, growth.] In certain 

 Fungi, a filament branching from 

 a hymenium without asci (bot.). 



periplasin (per'iplazm) n. [Gk. peri, 

 round ;^/^wa,somethingmoulded.] 

 The region of an oogonium outside 

 the oosphere, in Fungi (bot.). 



periplast (peYiplast) n. [Gk. peri, 

 round ; plastos, moulded.] The 

 attraction-sphere (cyt.) ; the ecto- 

 plasm of flagellates ; the firm cuticle 



of certain . Mastigophora ; inter- 

 cellular substance of tissues (zoo/.). 



peripneustic (peVipnu'stik) a. [Gk. 

 peri, round ;pneustikos,pert. breath- 

 ing.] Having stigmata arranged 

 along the sides of the body, normal 

 in insect larvae (zoo/.). 



periproct (per'iprokt) n. [Gk. peri, 

 round ; proktos, anus.] The surface 

 immediately surrounding the anus 

 of Echinoids (zoo/.). 



perisarc (peYlsark) n. [Gk. peri, 

 round ; sarx, flesh.] The tough 

 outer membrane of Hydrozoa (zoo/.). 



periscleral (peYiskle'ral) a. [Gk. 

 peri, round ; skleros, hard.] Appl. 

 a lymph-space external to the sclera 

 of the eye (anat.). 



perisome (peYisom) n. [Gk. peri, 

 round ; soma, body.] A body-wall ; 

 the integument of Echinoderms 

 (zoo/.). 



perisperm (peYisperm) n. [Gk. peri, 

 round ; sperma, seed.] The re- 

 mains of the nucellus of an ovule 

 when it is not all absorbed during 

 development of the embryo (bot.). 



perispore (per'ispor) n. [Gk. peri, 

 round; sporos, seed.] A spore- 

 covering ; the mother cell in Algae 

 spores (bot.). 



peristalsis (per'istal'sis) n. [Gk. peri, 

 round ; s tell fin, to place.] Move- 

 ment of the digestive tract, by which 

 food is digested and absorbed, by 

 means of involuntary muscles 

 (Phys.). 



peristaltic (pgr'istal'tlk) a. [Gk. peri, 

 round ; stellein, to place.] Af. 

 the movement by which fo 

 digested, forced along the aliment- 

 ary canal (pkys.). 



peristethium (peYiste'thmm) n. [Gk. 

 peri, round ; stethos, breast.] An 

 insect mesosternum. 



peristome (peVistom) n. [Gk. peri, 

 round; stoma, mouth.] The region 

 surrounding the mouth ; used in 

 connection with Mosses (bot.), Vorti- 

 cella, Actinozoa, Annulates, Insects 

 (zoo/.). 



perisystole (peVfsis'tole) n. [Gk. peri, 

 round ; systole, a drawing together.] 

 The interval elapsing between 

 diastole and systole of the heart 

 (phys.). 



perithecium (per'ithe'shium) n. [Gk. 



