INDEX 
Respiration, 7. 
Resting spore, 28, 
Reticulum, 67. . r 
Rhizocrinus loxotensis (illus.), 805. 
Rivalry, adaptations for, 135. 
Rookeries, fur-seal (illus.), 169. 
Rumen, 67. 
Sacculina (illus.), 187. 
Sacculina, adult and larva (illus.), 
195. 
Salamander, embryonic stages of 
(illus.), 87. 
Saliva, 67. 
Salmon leaping (illus.), 289. 
Salmo viridens (illus.), 145. 
Sarcoptes (illus.), 192. 
Sauba, ant mimicked by Membra- 
cide (illus.), 220. 
Scale, red orange (illus.), 196. 
Schilbeodes furtosus (illus.), 132. 
Schistocerca (illus.), 280. 
Scorpion (illus.), 127. 
Scorpion-fish (illus.), 132. 
Sea, a barrier to distribution, 288. 
Sea, faunal areas of, 304. 
Sea-anemone, 37; with alge in 
body (illus.), 178. 
Sea-cow (illus.), 277. 
Sea-cucumber, alimentary canal of 
(illus.), 70. 
Sea-squirt (illus.), 194. 
Sea-urchin, metamorphosis of (il- 
lus.), 96. 
Sea-urchins (illus.), 259. 
Seal, fur (illus.), 186; pups killed 
by parasite (illus.), 186; rook- 
eries (illus.), 169. 
Selection, artificial,120; natural,117. 
Self-defense, adaptations for, 128; 
instincts of, 245. 
Sensation, 8, 
327 
Senses, special, 224; of the simplest 
animals, 225. 
Sensorium, 241. 
Serphus (illus.), 141. 
Sex, 57; object of, 57; dimorphism, 
58. 
Shark-clinging fish (illus.), 125. 
Sheep, bighorn (illus.), 167; Rocky 
Mountain (illus.), 167. 
Sight, sense of, 237. 
Simplest animals, life of, 1. 
Siphonophora, 46. 
Skate, egg case of California barn- 
door (illus.), 140; egg of (illus.), 
79. 
Skin of man, tactile papilla of 
(illus.), 227. 
Smell, sense of, 229. 
Smelling organs, 229. 
Smelling pits of leaf-eating beetle 
(illus.), 280. 
Social life, 149. 
Sound-making, 235; organs, 235. 
South American realm, 301. 
Specialization, 66; of organs, 66. 
Special senses, 224. 
Species, altered by adaptation to 
new conditions, 276; debarred 
by barriers, 274; debarred by in- 
ability to maintain their ground, 
275; definition of, 279; relation 
of, to habitat, 283. 
Sperm cell, 35, 56. 
Sphinx moth, larva of (illus.), 215. 
Spicules, sponge, 33. 
Spiders (illus.), 212; nest-making 
habits of, 259. 
Sponges, 32. 
Spongin, 36. 
Spontaneous generation, 51. 
Spore, 15, 52; resting, 28. 
Sting-ray (illus.), 183. 
