GLOSSARY 701 



Proostraoon. The grooved or trough-like shell of certain cephalopoda. 



Propodium. The anterior portion of the molluscan foot. 



Prosoma. The primitive head of annelids. 



Prostate gland. The gland which secretes the fluid in which the spermatozoa 



are suspended. 



Prostomium. The anterior portion of the head of annelids. 

 Protopodite. The basal segment of a crustacean's leg. 



Protractor muscle^ A muscle which extends the organ to which it is attached. 

 Proximal. The position of a part of an organ towards the point of attachment 



. opposed to distal. 



Pseudopodium. A retractile locomotory process in sarcodins. 

 Pseudoscolex. The anterior end of certain tapeworms which lack a scolex. 

 Pseudostigmatic organs. A pair of club-shaped bristles on oribatid mites. 

 Pulsating vacuole. A globule of excretory fluid in many protozoans. 

 Pyrenoids. Deeply staining bodies in the chromatophores of Euglena. 



Rachis. The upper portion of the Pennatulacea, containing the polyps. 



Radial symmetry. Having the parts or organs arranged symmetrically about a 

 common center. 



Radials. Calcareous plates in crinoids above the basals. 



Eadius. One of the rays, the five main divisions of the echinoderm body. 



Radula., The band of calcareous teeth in the pharynx of most mollusks. 



Ray. One of the main divisions of the radiate body of echinoderms. 



Receptaculum seminis. A receptacle for sperm in the female animal. 



Rectum. The posterior division of the digestive tract. 



Respiratory tree. The paired branched diverticula of the rectum of holo- 

 thurians. 



Retractor muscles. Muscles which draw an organ towards its point of attach- 

 ment. 



Rhinophores. The posterior pair of tentacles in many opisthobranchs. 



Rhopalia. The sense organs or tentaculocysts of scyphomedusans. 



Ring canal. The central portion of the ambulacral system in echinoderms. 



Rostellum. A projection of the scolex of many tapeworms bearing hooks. 



Rostrum. A projection of the carapace in crustaceans; the cylindrical terminal 

 portion of a belamnite shell. 



Salivary glands^ Digestive glands at the anterior end of the digestive tract. 



Scleroblasts. The cells of the mesoglea of sponges which secrete the spicules. 



Scolex. The anterior end of a tapeworm containing the organs of attachment. 



Scutum. A shield on the dorsal surface of ticks. 



Scyphistoma. The hydroid generation of the Scyphomedusae. 



Secondary flagellum. A small branch of the tentacle in certain crustaceans. 



Segment. One of a number of serial divisions of an animal's body or of an 



organ. 

 Septum. A plate forming a division wall between two spaces; one of the 



radial calcareous plates of a stony coral. 

 Sessile. Fixed to one place, without locomotory powers of an animal; not 



on a stalk or stem of an organ. 

 Seta. A bristle. 



Sexual. Eeproduction through the agency of the two sexes. 

 Siphon. The organ through which water enters or leaves the mantle cavity in 



mollusks and ascidians. 

 Siphonal canal. A tubular prolongation of the lip of the aperture of many 



snail shells to enclose the siphon. 

 Siphonoglyph. A ciliated groove at one end of the mouth in the Anthozoa. 



