INDEX. 297 



Oils, dead, manufacture of, i. 120 



essential, chemical combinations forming, i. 97 



vegetable, i. 422 



formation of fixed and essential, artificially, i. 424 

 Oleandria, characters of the genus, i. 347 

 Oleandria neriiformis, structure of, i. 347 

 Olefiant gas, absorptive power of, i. 39, 40, 41 



amount of absorptive power, i. 41 



great absorption of, i. 47 



formation of, i. 97 



amount of carbon in, i. 105 



one of the illuminants in coal gas, i. 118 



chemical composition of, i. 128 

 Olefiant oil, i. 104 

 Olive oil, i. 422 



Onion, structure and mode of reproduction of, i. 388 

 Oniscus, common wood-louse or slater, structure of the, ii. 202 

 Onoclea, characters of the genus, i. 348 

 Onoclea sensibilis, characters and habitat of, i. 348 

 Oolina clavata, shell of, ii. 28 

 Opacity in liquids and solids synonymous with accord, i. 37 



causes of opacity, i. 37 

 Operculina, structure of, ii. 38, 46 



an instance of an individual combined with a common life, 



ii. 38. 



Ophioglossacese, characters of the group, i. 365 

 Ophioglossum, characters of the genus, i. 365 

 Ophioglossum vulgatum, structure and habitat of, i. 365 

 Ophionyx, structure of, ii. 173 

 Ophiuridae, or snake stars, structure of, ii. 172, 173 



power of reproducing rays, ii. 173 

 Ophrys apifera, or bee ophrys, structure and mode of reproduction of, 



i.397 



Ophrys, fly, structure and mode of reproduction of, i. 396 

 Opium, alkaloids obtained from, i. 427 



almost universal use of, in the East, i. 427 

 Orange, amount of radiant heat absorbed by the perfume of, i. 44 



fructification of the, i. 381 

 Oranges, fungus of decayed, i. 290 

 Orbitolite, characters of the, ii. 33 



a fossil gigantic one found in Canada, ii. 54 

 Orbitolites complanatus, structure of, ii. 33, 34 . 



