204 GLOSSARY. 



Sperm-sphere. A mass of spermatozoa in the earthworm. 



Spicules. Minute skeletal bodies. See Grantia. 



Spinneret. One of the organs by means of which a spider spins its thread. 



Spiracle. Breathing pore; external opening of the tracheal system. 



Spiral valve. The complicated posterior portion of the alimentary canal 



of a shark. 

 Spongin. The material of which the fibers of the commercial sponges 



are composed. 



Spore. A small reproductive body formed asexually. 

 Sporont. The detached stage of Gregarina. 

 Sporulation. The act of forming spores. 

 Stalk. A stem or a peduncle. 



Statoblast. Asexual reproductive body of certain Polyzoa. 

 Sternum. The 'ventral covering of a segment of an arthropod. 

 Stigma. One of the external openings of the trachea; one of the apertures 



in the pharynx of an ascidian. 



Stolon. An extension of the body-wall from which buds are developed. 

 Stomach. A division of the alimentary canal. 

 Stomach-intestine. A division of the alimentary canal that functions 



as both stomach and intestine. See earthworm. 

 Stomodaeum. The anterior portion of the alimentary canal that is ecto- 



dennal in origin. 



Stone canal. The tube that leads from the madreporic plate to the cir- 

 cular water canal in echinoderms. 

 Stylet. A small sharp instrument. 

 Sub-genital pits. The pouches adjacent to the gonads of the Discome- 



dusse, on the subumbrellar side. 

 Sub-neural gland. A glandular body in ascidians. 

 Sub-umbrella. The concave (oral) surface of a medusa. 

 Sulcus. A furrow or groove. 



Suture. An immovable union between plates or ossicles. 

 Swimmeret. Pleopod; an abdominal appendage of a crustacean 

 Swimming plate. One of the swimming organs of a ctenophore. 

 Synchronous. Happening at the same time. 

 Syphonoglyphe. A ciliated groove in some of the actinozoa. 

 Systemic heart. A heart that sends blood to the system. See squid. 



Tactile Capable of feeling. 



Tarsus. The segmented foot of an insect. 



Telson. Hinder division or segment of a crustacean. 



Tentacle. An elongated, unsegmented tactile organ 



Tentaculocyst. A sense organ of certain medusae. 



Tergum. The dorsal covering of a segment of an arthropod. 



Test. Shell of an echinoid; tunic of an ascidian. 



