GLOSSARY 219 
Prosternum: the ventral surface of the prothorax in insects; wasp, 3; 
grasshopper, 10. 
Prostomium : the anterior portion of the head of annelids, 62. 
Prothorax: the first thoracic segment in insects; wasp, 2; grasshopper, 9. 
Protopodite: the basal segment of a crustacean’s leg; crayfish or lobster, 32. 
Protractor muscle: a muscle which extends the organ to which it is 
attached; Nereis, 64; mussel, 91. 
Proximal: a position towards the point of attachment — opposed to distal. 
Pseudopodium : a retractile process in rhizopods, 194. 
Pulsating vacuole: a globule of excretory fluid in many protozoans; Para- 
mecium, 186; Vorticella, 189; Euglena, 193; Amoeba, 195. 
Pulvillus: an adhesive pad on the foot of insects; fly, 8; grasshopper, 12. 
Pupa: the stage in the life of a holometabolic insect when it is undergoing 
its metamorphosis. 
Racemose vesicles: minute diverticula of the ring canal in starfishes, 146. 
Radial symmetry: having the parts or organs arranged symmetrically 
about a common center. 
Radial tubes: a portion of the gastro-vascular space in the medusa, 167, 
178, 175. 
Radula: the band of calcareous teeth in the pharynx of gastropods and 
cephalopods; snail, 120; squid, 132. 
Ray: one of the main divisions of the radiate body of echinoderms, 141, 
150, 155. 
Receptaculum seminis: a receptacle for sperm in the female animal; grass- 
hopper, 16; spider, 27; crab, 44; snail, 118. 
Rectal glands: glandular structures in the rectum of certain insects, 15. 
Rectum: the posterior division of the digestive tract; grasshopper, 15; 
caterpillar, 21; crayfish or lobster, 39; Bugula, 86; mussel, 96; clam, 
110; snail, 118; squid, 131; sea cucumber, 156. 
Respiratory tree: a branched diverticulum of the rectum in holothurians, 
156. 
Retractor muscles: muscles which draw in an organ to which they are 
attached; Nereis, 64; mussel, 91; clam, 105. 
Rostrum : a projection of the carapace in crustaceans, 29: 
Salivary glands: digestive glands at the anterior end of the digestive tract; 
grasshopper, 15; snail, 118; squid, 131. 
Scaphognathite: the elongated epipodite of the second maxilla in certain 
crustaceans, 34. 
