192 GLOSSARY. 



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 di\ision of the alimentary canal that functions 

 as both stomach and intestine. See earthworm. 



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

 dermal 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-mnbrella. 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. 



