INDEX^ 



Abbott, C. H., 71 

 Achtenberg, H., 117 



Acids, effect on sperm suspensions, 269, 

 278 

 see also pH, HCl, H.SO4 

 Ackerman, L., 313 

 Acrididae, see Grasshoppers 

 Adsorption, of colloidal silver, 2c8-i2, 214, 

 222 

 of salts, 213-15 



of material from Procerodes experi- 

 ments, 233 

 Aeration, effect on crowded snail cultures, 



no, 112 

 Aestivation, of land isopods, 71 

 of quail, 72 



A gamer mis, see Nematodes 



Agar, W. E., 305 



Agglutination, of bacteria, 249 

 of spermatozoa, 272 



Aggregations, see also Crowding 



beneficial effects of, group defense, 102 

 catching food, 102 



stimulate growth, 147, 148, 149, 153 

 stimulate rate of regeneration in 



tadpoles, 148 

 increase rate of reproduction, 161, 



166, 178 

 increase survival, 181 

 decrease starfish autotomy, 182, 189, 



190 

 protect from colloidal silver, 201, 222 

 specificity of, 210 

 protect, from toxic salts, 213 



high temperature, 217 



from ultra-violet, 218 



hypotonic sea- water, 222 

 heterotypic protection, 228 

 factors contributing to, 231 

 in insects, 236 

 in bacteria, 253 

 in spermatozoa, 263, 284 

 see also Survival value of groups 

 breeding, 289, 358 

 of isopods, 65 



of mosquitoes and midges, 66 

 of frogs, 66 



of Ambysloma, 67 



of fish, 68 



of snakes, 68 



lunar periodicity in, 69 

 classification, 14, 35, 340 

 during "sleep," 74 



integration, 81, 87 

 effects on growth form, 311 



in aphids, 313 



in grasshoppers, 316 



in Drosophila, 331 

 formation, 38, 42, 65 



due to, social appetite, 46, 51, 52 

 instinct, 47, 48, 49, 52 



moisture control, 71, 181 

 harmful effects on growth, loi 



by food exhaustion, 102 



on bacterial growth, 103 



on Lymnaea, 108, 123 



on echinoderm larvae, no, 117, 153 



on Daphnia, no 



on tadpoles, 112 



on Hydra, 112 



on Planaria, 113 



on fish, 113, 116, 117 



summary of factors, causing, 118 



on grasshoppers, 319, 329 



on Drosophila, 332 

 harmful effects on longevity, 136 



of planarians, 140 



of Daphnia, 141 



in electrolytes, 141 



by pollution, 184 

 harmful effects on rate of reproduction, 

 120 



of Paramecium, 1 20 



of Stylonychia, 122 



of Daphnia, 126 



of hens, 1 26 



of Drosophila, 131 



of hookworms, 135 



of Cladocera, 306 

 origin of sex and, 290 

 origin of society and, 339, 340, 350, 363 

 types, 12, 36 



aestivation, 71 



hibernation, 70 



Aselltis, in nature, 52 



gyrinids, analysis of, 60 



caterpillars, analysis of, 48, 49, 50 



' Author citations in the index do not include reference to bibliography pages. 



413 



