220 INVERTEBRATE ZOOLOGY 



Sclerite: a small plate forming a portion of the cuticula of a segment 



in insects. 

 Scolex : the anterior end of a tapeworm, 80. 

 Scutellum : a small sclerite in the tergum of the thoracic segments in 



insects. 

 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 ; Nereis, 63 ; 



earthworm, 69 ; mussel, 92 ; clam, 106. 

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



Bugula, 85 ; oyster, 99 ; Molgula, 135 ; tubularian, 163 ; campanularian, 



169 ; Grantia, 181 ; Vorticella, 188 : not on a stalk or stem — of an 



organ, 46. 

 Seta : a bristle ; Nereis, 61 ; earthworm, 67. 

 Setigerous glands : glands which secrete setae, 73. 

 Sexual : reproduction through the agency of the two sexes. 

 Shell gland : the kidney of entomostracans ; copepod, 55 ; Daphnia, 57. 

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



in mollusks and ascidians ; mussel, 92 ; clam, 106 ; squid, 124 ; Mol- 

 gula, 135. 

 Siphonoglyph : a ciliated groove in the angle of the gullet in Anthozoa, 178. 

 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 semi- 

 nal receptacle, 72. 

 Spermatophore : a capsule or mass of spermatozoa ; copepod, 55 ; snail, 121 ; 



squid, 133. 

 Spermatozoon : the male sexual cell. 

 Sperm-duct : the vas deferens, 27, 71. 

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



vesicle, 71. 

 Sperm-sphere : a mass of spermatozoa in the earthworm, 73. 

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

 Spinnerets : the appendages on a spider from which the silk exudes, 25. 

 Spiracle : an external opening in the tracheal system ; wasp, 3 ; fly, 8 ; 



grasshopper, 11 ; caterpillar, 21 ; spider, 26. 

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



hydroid ; tubularian, 163 ; campanularian, 169. 

 Sternite : the ventral portion of an abdominal segment in insects ; wasp, 3; 



grasshopper, 10. 



