INDEX 
Mouse-fish in gulf-weed (illus), 208. 
Mt. Orizaba (illus.), 300. 
Multiplication, 50; of animals, 
114; simplest method of, 53; 
slightly complex methods of, 54, 
Murres, Pallas’s (illus.). 165. 
Mussel, alimentary canal of (illus.), 
72. 
Mutual aid, 163. 
Narcine brasiliensis (illus.), 185. 
Natural selection, 117. 
Neotropical realm, 301. 
Nerve cells, 240. 
Nerve fibers, 240. 
Nest-making habits of birds, 264; 
of fishes, 264; of insects, 262; 
of invertebrates, 258; of spiders, 
259; of vertebrates, 264. 
Nest of Baltimore oriole (illus.), 
267; of beavers (illus.), 269; of 
Californian bush-tit (illus.), 270; 
of Cteniza californica (illus.), 
261; of pocket-gopher (illus.), 
271; of rufus humming - bird 
(illus.), 265, 266; of tailor-bird 
(illus.), 268; of trap-door spider 
(illus.), 261; of turret - spider 
(illus.), 262. 
Nokee (illus.), 182. 
Nomeus gronovit (illus.), 175. 
North Temperate realin, 299. 
Nuclear membrane, 3. 
Nucleus, 3. 
Obelia, alimentary sac of (illus.), 
69. 
{Hsophagus, 67. 
Omasum, 67. 
One-celled animals, 2. 
Organ, 68; auditory, of cray-fish 
(illus.), 233; of cricket (illus.), 
22 
325 
234; of grasshopper (illus.), 234; 
of mosquito (illus.), 285; of mol- 
lusk (illus.), 233. 
Organic matter, 112. 
Organs, auditory, 282; of smell, 
229; of sound-making, 235; of 
taste, 228; of touch, 226; spe- 
cialization of, 66; vestigial, 147. 
Oriole, Baltimore, nest of (illus.), 
267. 
Ornithotomous sutorius, nest of, 
268. 
Osprey Falls (illus.), 285, 
Otolith, 282. 
Ox, alimentary canal of (illus.) 67. 
Oxygen, necessary to animal life, 
107. 
Pagurus (illus.), 176. 
Pandorina, 26. 
Pandorina sp. (illus.), 26. 
Pandorina morum (illus.), 27. 
Papilio, chrysalid of (illus.), 205, 
Papilla, tactile, of skin of man 
(illus.), 227. 
Papille, 67. 
Paramecium, 9. 
Paramecium aurelia (illus.), 10. 
Paramecium caudatum (illus.), 11. 
Paramecium plutorinum (illus.), 
11. 
Parasite of caterpillar (illus.), 190; 
relation to host, 179. 
Parasites, simple structure of, 181. 
Parasitism, 179; kinds of, 180. 
Parthenogenesis, 60. 
Patagonian realm, 302. 
Pediculus (illus.), 188. 
Pelagic fauna, 304. 
Pelican, brown (illus.), 125. 
Peneus, adult and larva (illus.), 
195. 
