202 INVERTEBRATE ZOOLOGY 



Peritoneum: the membrane lining the body-cavity. 



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

 mouth; grasshopper, 13; Nereis, 58; earthworm, 65; Bugula, 80; 

 snail, 107 ; squid, 121 ; Molgula, 126. 



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

 face waters of the sea or of fresh water. 



Pleopod: an abdominal appendage in crustaceans, 26. 



Pleurobranch : a gill attached to the body-wall in crustaceans ; crayfish or 

 lobster, 29 ; crab, 37. 



Pleurum: the lateral surface of the thorax in insects; wasp, 3; grass- 

 hopper, 8. 



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

 tain insects, 9. 



Podobranch: a gill attached to the leg in crustaceans, 29. 



Polyp: a sessile individual in the Cnidaria; Hydra, 145; tubularian, 149 ; 

 campanularian, 156. 



Polypide: the soft parts of a bryozoan, 79. 



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



Proboscis: a prehensile organ in certain worms, usually a portion of the 

 pharynx ; Nereis, 55 ; planarian, 70 : the beak-like mouth-parts of cer- 

 tain insects. 



Proglottis : a tapeworm segment, 74. 



Prosoma: the primitive head of annelids made up of the prostomium and 

 the metastomium, 56, 62. 



Prostate gland : the gland which secretes the fluid in which the spermatozoa 

 are suspended; grasshopper, 15; squid, 122. 



Prosternum : the ventral surface of the prothorax in insects ; wasp, 3 ; 

 grasshopper, 8. 



Prostomium: the anterior portion of the head of annelids, 56, 62. 



Prothorax : the first thoracic segment in insects ; wasp, 2 ; grasshopper, 7. 



Protopodite: the basal segment of a crustacean's leg; crayfish or lob- 

 ster, 26. 



Protractor muscle: a muscle which extends the organ to which it is 

 attached ; Nereis, 58 ; mussel, 85. 



Protrochula : the stage in the development of a typical trochozoan immedi- 

 ately preceding the trochophore stage. 



Proximal : a position towards the point of attachment opposed to distal. 



Pseudopodium : a retractile process in rhizopods, 174. 



Pulsating vacuole : a globule of excretory fluid in many protozoans ; Para- 

 mecium, 166; Vorticella, 169; Euglena, 173; Amoeba, 175. 



