240 GLOSSARY 



Sessile : fixed to one place, without locomotory powers — of an animal ; 

 not on a stalk or stem — of an organ. 



Seta: a bristle. 



Sexual: reproduction through the agency of the two sexes. 



SheU gland: the kidney of entomostracans. 



Siphon: the organ through which water enters or leaves the mantle cavity 

 in mollusks and ascidians. 



Siphonoglyph: a ciliated groove in the angle of the gullet in Anthozoa. 



Somite : one of the serial, homologous body segments which form the body 

 of an articulate animal. 



Spermatophore: a capsule of spermatozoa. 



Spermatozoon: the male sexual cell. 



Sperm duct: a duct leading from the testis. 



Sperm receptacle: a sac for the storing of sperm in the female animal. 



Sperm sac: a sac for the storing of sperm in the male animal, a seminal 

 vesicle. 



Sperm sphere: a mass of spermatozoa in the earthworm. 



Spicule: a minute, calcareous or siliceous body in sponges and echinoderms. 



Spinnerets: the appendages on a spider from which the silk exudes. 



Spiracle: an external opening in the tracheal system. 



Sporosac: a sessile medusoid, one which remains attached to the parent 

 hydroid. 



Sternum: the breastbone. 



Stigmata: the respiratory openings in the pharyngeal wall in Molgula. 



Stipes: a division of the maxilla in insects. 



Stomach: a division of the digestive tract. 



Stomach pouch: a diverticulum of the stomach. 



Stone canal: a tube joining the madreporite with the ring canal in echi- 

 noderms. 



Submentum : the basal segment of the labium in insects. 



Subneural gland: a glandular body in ascidians. 



Subumbrella: the oral surface of a medusa. 



Supporting layer: the noncellular layer between the ectoderm and ento- 

 derm in Hydrozoa. 



Swimmeret: an abdominal appendage of a crustacean, a pleopod. 



Symbiotic: the living together of two dissimilar organisms, each being 

 dependent upon the other. 



Systemic heart: the median heart of the squid. 



Tactile: relating to the sense of touch. 



Tarsus: the foot of an insect or a spider; the ankle of vertebrates. 



Telson: the terminal segment of a crustacean. 



Tentacle: an elongated, unsegmented tactile organ. 



Tergum: the dorsal surface. 



