INDEX 



Select ivitv, in Amoeba, 234 



Self-fertilization, 174; prevention of, in 



hermaphrodites, 534 

 Semicircular canals, 108 

 Semicircular ducts, 90, 102, 108 

 Seminal fluid, 130, 144 

 Seminal receptacle, of arthropods, 533; of 



cravhsh, 435-436; of earthworm, 411; of 



planarians, 321 

 Seminiferous tubules, 129 

 Sense organs, 91; of crayfish, 433; of jellyfish, 



523; of locust, 451 

 Sensory centers, 104 

 Sensory-neuro-muscular system, of earthworm, 



410;' of hvdra, 295, 297; of metazoans, 



522 525 

 Sensory neuron, 98 

 Sensory root, 98 

 Septa, 392 

 Septa, in annelids, 396; in earthworm, 406; in 



Metndium, 306, 307; in Nereis, 399 

 Serial homology, 429 

 Serological evidence of relationships, 543 

 Serology, 635 

 Serpent stars, 486, 497 

 Serum, 65; and immunity, 635 

 Setae, 396, 403, 405 

 Seymouria, 568 

 Sex, determination of, 208-211; reversal of, 



211 

 Sex chromosomes, 4 1 , 209 

 Sex hormones, 26 



Sex-linked inheritance, 181, 190, 199 

 Sexual reproduction, 141, 530 

 Sexually indifferent stage, 132 

 Sharks, 541, 556, 557; as persistent primitive 



types, 631; of Devonian Period, 555, 559; 



origin and ancestry of, 557 

 Shelford, Victor, 611 

 Shell, of chitons, 381; of egg, 144; of pelecy- 



pods, 377 

 Shipworms, 381 

 Shock, 66 



Shoulder girdle, 93 

 Shrews, 579 

 Shrimp, 440 

 Silkworm, 469 

 Silurian Period, and amphibians, 561; and 



fossil ostracoderms, 555 

 Silverfish, 458 

 Simple epithelium, 59 

 Simple lipids, 26 



Simple sugars, see Monosaccharides 

 Sinanlhropus, see Pithecanthropus pekinensis 

 Sinuses, in crayfish, 432; in open circulatory 



systems, 514 

 Siphon, of squid, 389 

 Siphon retractor muscles, in Venus, 371 

 Siphonoglyph, of Melndnm, 307 

 Siphonophora, 303, 528 



Siphonops, 215, 565 



Siphons, of ascidians, 545; of pelecypods, 370, 



371, 379 

 Sipunculoidea, 216, 221 

 Six-hooked embryo, 337 

 Skate, prickly, 556 

 Skates, 541, 557; and rays, 557 

 Skeletal muscle, see Striated muscle 

 Skeletal structures of invertebrates, 527-529 

 Skeletal system, 87, 91-95 

 Skeleton, 91-93; appendicular, 93; axial, 92; 



of Chondrichthyes, 557; of Sarcodina, 



238 

 Skin, 56, 60, 82 

 Skin breathing, 562 

 Skull, of early man, 639 

 Sleep, 103 



Sleeping sickness, African, 244 

 Sloth, 580 

 Slug, 385, 386 



Small granular component, 20 

 Small intestine, 48, 49, 50, 69, 71, 72, 75 

 Snails, 606; of Hawaii, 652; see also Gastropoda 

 Snakes, 541, 571 

 Social organization, of bees and wasps, 470- 



475; of termites, 458 

 Social sciences, 7 

 Social wasps, 470 

 Soft palate, 48 

 Soft-shelled crabs, 430 

 Soft-shelled turtle, 567, 570 

 Solaster, 497 

 Solenocyte, 519, 520 

 Solitary wasps, 470 



Solutrean culture, weapon point from, 645 

 Somatic cells, 58, 647; of Pleodonna, 267; of 



Hydra, 292 

 Somite reduction, in arthropod evolution, 485 

 Somites, of annelids, primary and secondary, 



401; of A'^rm, 398 

 South Africa, lungfish of, 558 

 South America, apodous amphibians in, 565; 



Camelidae of, 631; horses of, 625; lungfish 



of, 558 

 Sow bug, 439, 440, 485 

 Spallanzani, Lazaro, 143 

 Spatanous, 501, 502 

 Special creation, 633 

 Specialization of cells, 619 

 Speciation, isolation as factor in, 652 

 Species, definitions of, 217, 651; maintenance 



of, by reproduction, 529 

 Species concept, 216 

 Sperm, see Spermatozoon 

 Sperm whale, 589 

 Spermatids, 137 



Spermatogenesis, 135-138; in Hydra, 298 

 Spermatogonium, 136 

 Spermatophores, of crayfish, 435; of squid, 



390 



704 



