GLOSSARY 577 



pleural cavity. That part of the coclom in mammals which contains the lungs; the 



lining membrane is the pleura, 

 plexus. A network of nerves. 



Pliny (plln' I); Caius Plinius Secundus, the Elder. Roman naturalist; 23-79. 

 pneumo (nu' m6). G.; air, breath, consequently soul or spirit, 

 pod (pod). G.; foot. 

 polar body. A nonfunctional cell produced in the maturation divisions of an egg 



cell, 

 polarity (p6 lAr' I tl). That condition in a body connected with the dominance of 



one part over another, or in a conducting substance that which determines the 



direction in which conduction will take place. 

 poly (p6l' I). G.; many. 



polyandry (p6l i ftn' dri). The mating of one female with several males, 

 polygamy (p6 llg' a mT). The mating of several females with one male, 

 polymorphism (p5l I mor' fiz'm). The existence of more than one form of the same 



species; adj., polymorphic; if there are only two forms, the condition is spoken of 



as dimorphism, 

 polyp (pol' Ip). An attached coelenterate. 

 portal system, A capillary system interposed in the course of a vein; when used 



without qualification it is that part of the venous system which passes blood 



through the liver. 

 positive response. A response in which an organism turns or moves toward the 



stimulus. 

 post- (post). L.; after, behind, 

 posterior (p6s te' ri er). Behind; in a bilaterally symmetrical aninuil with the axis 



horizontal, away from the head. 

 precocial (pre ko' shal). Term applied to a bird the young of which have down, leave 



the nest, and are active as soon as they have hatched. 

 predaceous (pre da' shvis). Preying on other animals; the condition is known as 



predatism (pred' a tiz'm). 

 preformation (pre for ma' shtin). The conception formerly held that the parts of an 



organism were preformed in the germ cell. 

 primates (pri'mats). Animals belonging to the mammalian order Primates (pri- 

 ma' tez). 

 primordial (pri mor' dl Hi). The first in order, original, 

 pro- (pro). G.; before. 

 proboscis (pro b6s' is). A forward extension of the head, especially of the snout in 



mammals. 

 proctodeum (pr5k t6 de' tim). An invagination of the surface of an embryo which 



meets the posterior end of the archenteron and forms that portion of the alimen- 

 tary canal just before the anus. 

 proglottid (pro glot' id). One of the individuals in a tapeworm colony, 

 pronephros (pro nff ros). A primitive vertebrate kidney, functional only in the 



liag; adj., pronephric. 

 pronucleus (pro nu' kle us). The nucleus of a sperm cell after it has entered an egg 



cell and also that of the egg cell itself before the two have united in fertilization; 



they are termed, respectively, male and female pronuclei. 

 prophase (pro' faz). The first phase in mitosis, lasting until the chromosomes are 



lined up in the equator of the spindle, 

 proprioceptor (pr6 prI 5 s6p' tlir). A receptor contained within the tissues of the 



body and stimulated by conditions in the tissues themselves. 

 prostate (pr6s' tat) gland. A gland connected with the male reproductive system 



which produces a secretion that stimulates the sperm cells to activity. 



