228 
152; ambulacral system, 153 ; nerv- 
ous system, 154; circulatory system, 
154. 
Sessile ciliate, 188. 
Shrimp, freshwater: external parts, 
48; appendages, 49. 
Simple ascidian, 135. 
Slipper animalcule, 184. 
Snail, see Land snail. 
Sow-bug: external parts, 46; append- 
ages, 47. 
Spider, 24. 
Spongiaria, 181. 
Squid: external anatomy, 123; mantle 
cavity, 125; excretory system, 127; 
circulatory system, 129; respiratory 
system, 129; digestive system, 130; 
reproductive system, 182; nervous 
system, 133; pen, 134. 
Starfish: external parts, 141; digest- 
ive system, 145; reproductive sys- 
tem, 145; ambulacral system, 146 ; 
nervous system, 147; circulatory 
system, 148. 
Strongylocentrotus, 149. 
Sycon sponge, 181. 
INVERTEBRATE ZOOLOGY 
Taenia crassicollis, 80. 
Taenia saginata, 80. 
Taenia serrata, 80. 
Talorchestia, 48. 
Tapeworm: external form, 80; pro- 
glottids, 81; encysted tapeworm, 
83. 
Trachomedusa, 175. 
Tubularian hydromedusan: alterna- 
tion of generations, 163; hydroid 
stage, 163 ; medusoid stage, 167. 
Tunicata, 135. 
Turbellaria, 76. 
Unio, 89. 
Venus mercenaria, 103. 
Vorticella: general form, 188; repro- 
duction, 190; conjugation, 191. 
Vorticellide, 188. 
Wasp: external parts, 1; mouth-parts, 
13. 
Zoothamnium, 188. 
