238 GLOSSARY 



Paragnatha: delicate lamellae just behind the mandibles in the crayfish 

 or the lobster. 



Parapodium: the appendage of annelids. 



Parasite: an animal which attaches itself to another and lives upon its 

 nutritive fluids. 



Parenchyma: a vesicular connective tissue which fills the body cavity of 

 flatworms and leeches. 



Parthenogenesis: reproduction by means of unfertilized eggs. 



Pectoral: relating to the thorax or breast. 



Pedicellariae: minute pincer-like organs present on the external surface of 

 starfishes and sea urchins. 



Pedipalps: the second pair of appendages in the Arachnida. 



Pelvic: relating to the region of the hind Hmbs. 



Pen: the shell of the squid. 



Pericardium: the membrane surrounding the heart. 



Periopods: the thoracic appendages posterior to the maxillipeds in crus- 

 taceans. 



Periostracum: the outer layer of the molluscan shell. 



Periphery: the outer surface of a body. 



Periproct: the region immediately around the anus. 



Perisarc: the cuticular outer covering of a hydroid. 



Peristome: a membrane surrounding the mouth in echinoderms. 



Peristomium: the posterior portion of the head in most annelids, consisting 

 of the metastomium and the anterior somites of the metasoma. 



Peritoneum: the membrane Hning the body cavity. 



Pharynx: the division of the alimentary tract immediately back of the 

 mouth. 



Plankton: a collective term referring to all small forms of life in the surface 

 waters of the sea or of fresh water. 



Planula: the larva of many Coelenterata. 



Pleopod: an abdominal appendage in crustaceans. 



Pleurobranch: a gill attached to the body wall in crustaceans. 



Plexus: a network. 



Podical plates: paired sclerites at the posterior end of the abdomen in 

 certain insects. 



Podobranch: a gill attached to the leg in crustaceans. 



Polian vesicle : a sac extending from the ring canal in echinoderms. 



Polymorphism: the condition in which a species exists in several distinct 

 forms. 



Polyp : a sessile individual of any of the lower animals. 



Polypide: the soft parts of a bryozoan. 



Posterior: at or toward the hinder end of an animal. 



Proboscis: a prehensile or sucking organ in certain animals, usually a por- 

 tion of the pharynx. 



