The American Naturalist, Volume 26, Part 2Essex Institute, 1892 |
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abundant acid acquired characters American animals annelids appear augite bacteria biotite blastopore body bone Botany brain Bull carbon carbonic acid cavity cells cheese chromatin cleavage color contains crystals described Dipnoi dorsal ectoderm embryo evidence evolution fact fauna fertilization fish formation function ganglion gemmule genus Geol Geological germ germ-cells habits hereditary heredity insects interesting Jour Lake larva larvæ later limestone Lophiodon lower mass ment mineral molar mound Museum nature Nemaha counties normal nucellus nucleus observed olivine organs original ovum oxygen paper peculiar plagioclase plants plates polar bodies pollination polyspermy portion posterior prehistoric premolars present Prof Protohippus protoplasm quartz recently region respiration River rocks sections shell heaps snakes species specimens sperm spermatozoon stage structure substance surface tail theory tibiæ tion tissue variations ventral Weismann
Popular passages
Page 892 - Herbert Spencer defines life as " the continuous adjustment of internal relations to external relations ;
Page 566 - It follows as an unprejudiced conclusion from our present evidence that upon Weismann's principle we can explain inheritance but not evolution, while with Lamarck's principle and Darwin's selection principle we can explain evolution, but not, at. present, inheritance. Disprove Lamarck's principle and we must assume that there is some third factor in evolution of which we are now ignorant.
Page 1010 - somatogenic ' characters cannot be transmitted, or rather, that those who assert that they can be transmitted, must furnish the requisite proofs. The somatogen1c characters not only include the effects of mutilation, but the changes which follow from increased or diminished performance of function, and those which are directly due to nutrition and any of the other external influences which act upon the body.
Page 1020 - ... to convey through the medium of the sounds. They wait for and expect an answer, and if they do not receive one they frequently repeat the sounds. They usually look at the person addressed, and do not utter these sounds when alone or as a mere pastime, but only at such times as some one is present to hear them, either some person or another monkey. They understand the sounds made by other monkeys of their own kind, and usually respond to them with a like sound. They understand these sounds when...
Page 892 - These metabolic changes are brought about, in the main, at the expense of energy, and they represent, in fact, successive transformations of energy from the active to the potential form, and a final reconversion to heat, which leaves the body in various ways. The animal machine is, in effect, a heat-engine...
Page 1014 - The introduction of elementary physics into the later years of the programme as a substantial subject, to be taught by the experimental or laboratory method, and to include exact weighing and measuring by the pupils themselves.
Page 667 - ... half an embryo with a hot needle in the first stages of segmentation and followed the other half through the stages of subsequent development. Another clever experimenter has turned fertilized ova upside down during the early stages of development, and shown how the protoplasmic pole and yolk pole forcibly change places. Driesch has traced the connection and meaning of the first plane of cleavage in the embryos of echinoderms, and has succeeded in raising a small adult from half an embryo artificially...
Page 972 - After complete fixation the paraffin is melted by putting the slide inside the oven and then washed off with turpentine or xylol. One of the great advantages of this method is the perfect ease and safety with which it allows sections on the slide to be manipulated, so that the most various stains and reagents can be applied successively to a slide, eg, the complicated processes used to demonstrate bacteria in the tissues can be applied, with the certainty, moreover, that there is nothing on the slide...
Page 652 - That before union the hereditary substance in each is greatly reduced. 3. That there is no line between male and female, the conjugating cells are simply in a similar physiological condition wherein a mingling of hereditary characteristics affords a new lease of life. As Maupas says : " Les differences appelees sexuelles portent sur des faits et des phenomenes purement accessoires de la fecondation. La fecondation cousiste uniquement dans la reunion et la copulation de deux noyaux semblables et equivalents,...
Page 657 - ... substance of a normal nucleus. In the ovary three of these daughter cells abort and the fourth forms a true ovum; in the sperm gland, however, all four daughter cells form spermatozoa. We may thus consider the polar-cell problem as in all probability settled; the whole process is probably an inheritance or survival of a primitive condition in which all four ova, like the four spermatozoa, were fully functional. The relation between the chromatin and heredity. — We have just seen that the last...