GLOSSARY 



263 



Polymorphism. Many distinct forms of individuals within a single 

 species. 



Polyp. An individual of a hydroid stage of a coelenterate. 



Postcava. In some invertebrates, a blood vessel which leads to the 

 heart from the posterior portion of the body, as in the squid. 



Posterior. Hinder; anal end. 



Precava. In some invertebrates, a blood vessel which leads to the 

 heart from the anterior end of the body. 



Primary mesentery. A mesentery which extends from the body wall 

 to the actinopharynx in Actinozoa. 



Proboscis. Applied to various tubelike organs around the head some- 

 times capable of being everted or protruded. 



Proglottid. One of the numerous "segments" which are formed by the 

 scolex and which, together with the scolex, make up a tapeworm. 



Propod. The next to the last segment, fourth, of a typical crustacean 

 endopod. 



Prosopyle. One of the pores through which water passes from an in- 

 current to a radial canal in most sponges. 



Prostomium. The anterior process which overhangs the mouth of an 

 annelid. 



Prothorax. Anterior division of the thorax of an insect. 



Protomerite. The anterior part of a eugregarine, e. g., Gregarina. 



Protopod. The basal portion of a crustacean appendage. It consists 

 of two segments, a basal coxopod and a distal basipod. The latter 

 frequently bears both an exopod and an endopod. In some cases 

 it also bears an epipod or bract and a gill. 



Proximal. Nearest to the point of origin or attachment. Converse of 

 distal. 



Pseudopodium. A temporary protrusion of the protoplasm of a cell. 

 Found in all Sarcodina and in certain tissue cells of higher animals. 



Pyloric stomach. Posterior or second division of the stomach. 



Radially symmetrical. The condition of having similar parts radially 



arranged about a central axis; as in a jelly fish. 

 Radius. One of the parts of the jaw apparatus of an echinoid; from 



center to periphery. 

 Radula. The flexible, tooth-bearing, ribbon-like membrane of an odon- 



tophore. 

 Ray. One of the arms of a starfish or a brittle star. 

 Rectum. The posterior division of the alimentary canal. 

 Renal organ. An organ which excretes nitrogenous wastes and other 



materials. 

 Reservoir. The place where anything is stored; the poison sac of a bee. 



