A Text-book of biology, for students in medical, technical and general coursesLea & Febiger, 1913 - 285 páginas |
Índice
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Palavras e frases frequentes
adult ameba amitosis animal behavior B. G. Smith bacteria become biology blood body carbohydrates carbon cells cent centrosome changes CHAPTER character chemical chromatin chromosomes corpuscles Cryptobranchus cytoplasm definite differentiation digestive disease division dorsal duct earthworm ectoderm embryo enzymes evolution existence female ferments fertilization fibers frog germs given gland grow growth habit heredity higher animals hydra illustrate individuals insects intestine Journal of Morphology kidney known large number larvæ layer living protoplasm living substance living things male membrane metabolism method movement muscles nature nematocyst nerve nitrogen nucleus organs ovaries oviduct ovum oxygen paramecium parasites parent Phylum physiological posterior produced pronucleus protein protoplasm protozoa region relation reproduction result skin somites species spermatocyte spermatozoon sperms spindle spores Sporotrichosis stage stimulus structure tadpole tentacles term tissue unicellular urinogenital usually vacuoles variation ventral vertebrates W. E. Castle worm yeast
Passagens conhecidas
Página 182 - I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny.
Página 183 - The mistletoe is dependent on the apple and a few other trees, but can only in a far-fetched sense be said to struggle with these trees, for, if too many of these parasites grow on the same tree, it languishes and dies. But several seedling mistletoes, growing close together on the same branch, may more truly be said to struggle with each other.
Página 182 - We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations given to him by the hand of Nature. But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man's feeble efforts as the works of Nature are to those of Art.
Página 182 - Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species...
Página 183 - But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to be dependent on the moisture.
Página 217 - But stood before him glorified, Shining and tall and fair and straight As the pillar that stood by the Beautiful Gate, — Himself the Gate whereby men can Enter the temple of God in Man.
Página 182 - ... offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.
Página 182 - I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man's power of selection. But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient
Página 222 - There is not a single species in which the sting is given with invariable accuracy. To judge from results they scarcely sting twice alike, since the victims of the same wasp may be killed at once or live from one day to six weeks, or perhaps ultimately recover.
Página 182 - Owing to this struggle, variations, however slight and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the offspring.