702 GLOSSARY 



Siphonozooid. Eudimentary zooids through which water flows into the ento- 

 dermal canals in the Pennatulacea. 



Siphuncle. The tubular portion of a nautilus' body which extends through 

 the chambers. 



Somite. One of the serial, homologous body-segments which form the body of 

 an articulate animal. 



Spermatheca. A sac for the storing of sperm in the female animal, a seminal 

 receptacle. 



Spermatophore. A capsule or mass of spermatozoa. 



Spermatozoon. The male sexual cell. 



Sperm-duct. The vas deferens. 



Sperm-sac. A sac for the storing of sperm in the male animal, a seminal 

 vesicle. 



Spicule. A minute calcareous or silicious body in sponges and echinoderms. 



Spinnerets. Appendages at the hinder end of a spider containing the openings 

 of the silk glands. 



Spiracle. An external opening in the tracheal system in arthropods. 



Spire. The portion of a snail shell above the large lowest whorl. 



Spongin. The substance composing the elastic fibers of a sponge. 



Spongioblasts. The mesoglea cells which form the elastic fibers of a sponge. 



Sporont. The sporulating stage of a sporozoan. 



Sporosac. A sessile medusoid, one which remains attached to the parent 

 hydroid. 



Statoblast. Disc-like buds in fresh-water Bryozoa which live through the 

 winter. 



Sternum. The ventral portion of the cepholothorax surrounded by the legs in 

 spiders. 



Stigmal plate. A plate surrounding the spiracle in certain mites. 



Stigmata. The respiratory openings in the pharyngeal wall in ascidians. 



Stomach. A division of the digestive tract in which digestion goes on. 



Stomach pouch. A diverticulum of the stomach. 



Stone canal. A tube joining the madreporite with the ring canal in echino- 

 derms. 



Streptoneurous gastropods. Snails in which the pleuro-visceral connections cross 

 each other. 



Strobilation. The process of terminal budding. 



Stylets. Calcareous needles in the proboscis of hoplonemerteans. 



Subchelate. A pinching claw formed by the bending of the terminal segment 

 over the next one. 



Subcuticula. The tissue beneath the cuticula in trematodes and cestodes. 



Subgenital pocket. A pocket in the subumbrella of many scyphomedusans. 



Subneural gland. A glandular body in ascidians. 



Subumbrella. The oral surface of a medusa. 



Summer eggs. Thin-shelled eggs produced by parthenogenetic females of cer- 

 tain crustaceans, usually in the summer. 



Supporting layer. The non-cellular layer between the ectoderm and entoderm 

 in Hydrozoa. 



Swimmeret. The abdominal appendage of a crustacean, a pleopod. 



Symbiotic. The living together of two dissimilar organisms, each being depend- 

 ent upon the other. 



Systemic heart. The median heart of the squid. 



Tactile. Relating to the sense of touch. 



Tarsus. The segmented foot of an arthropod. 



Telson. The terminal segment of a crustacean or arachnoid. 



Tentacle. An elongated tactile organ. 



