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Export to Excel select * from OriginOfSpecies where ordinal = '40' order by description limit 4 (Page 1: Row)
subject
title
ordinal
description Desending Order (top row is first)
06 - Difficutiles in Theory 06-08 - Means of Transition 40 According to this view it may be inferred that all vertebrate animals with true lungs are descended by ordinary generation from an ancient and unknown prototype, which was furnished with a floating apparatus or swimbladder.

We can thus, as I infer from Owen's interesting description of these parts, understand the strange fact that every particle of food and drink & which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs, notwithstanding the beautiful contrivance by which the glottis is closed. In the higher Vertebrate the branchiae have wholly disappeared- but in the embryo the slits on the sides of the neck and the loop-like course of the arteries still mark their former position.

But it is conceivable that the now utterly lost branchiae might have been gradually worked in by natural selection for some distinct purpose: for instance, Landois has shown that the wings of insects are developed from the tracheae; it is therefore highly probable that in this great class organs which once served for respiration have been actually converted into organs for flight.
gills
gills

Swim Bladder
Swim Bladder

lungs
lungs

wings
wings
06 - Difficutiles in Theory 06-13 - Summary: The Law of Unity of Type and of the Conditions of Existence Embraced by the Theory of Natural Selection 40 Although the belief that an organ so perfect as the eye could have been formed by natural selection, is enough to stagger any one; yet in the case of any organ, if we know of a long series of gradations in complexity, each good for its possessor, then, under changing conditions of life, there is no logical impossibility in the acquirement of any conceivable degree of perfection through natural selection.
eye
eye


In the cases in which we know of no intermediate or transitional states, we should be extremely cautious in concluding that none can have existed, for the metamorphoses of many organs show what wonderful changes in function are at least possible.

For instance, a swimbladder has apparently been converted into an air-breathing lung.
Swim Bladder
Swim Bladder

lungs
lungs


The same organ having performed simultaneously very different functions, and then having been in part or in whole specialised for one function; and two distinct organs having performed at the same time the same function, the one having been perfected whilst aided by the other, must often have largely facilitated transitions.
13 - Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Or 13-03 - Rules and difficulties in classification, explained on the theory of descent with modification 40 Any one of these characters singly is frequently of more than generic importance, though here even when all taken together they appear insufficient to separate Cnestis from Connarus.' To give an example amongst insects, in one great division of the Hymenoptera, the antennae, as Westwood has remarked, are most constant in structure; in another division they differ much, and the differences are of quite subordinate value in classification; yet no one probably will say that the antennae in these two divisions of the same order are of unequal physiological importance.

cnestis
cnestis

connarus
connarus

hymenoptera
hymenoptera


Any number of instances could be given of the varying importance for classification of the same important organ within the same group of beings.

Again, no one will say that rudimentary or atrophied organs are of high physiological or vital importance; yet, undoubtedly, organs in this condition are often of high value in classification.

No one will dispute that the rudimentary teeth in the upper jaws of young ruminants, and certain rudimentary bones of the leg, are highly serviceable in exhibiting the close affinity between Ruminants and Pachyderms.

Robert Brown has strongly insisted on the fact that the rudimentary florets are of the highest importance in the classification of the Grasses.
04 - Natural Selection 04-13 - Convergence of Character 40 As far as mere inorganic conditions are concerned, it seems probable that a sufficient number of species would soon become adapted to all considerable diversities of heat, moisture, &c.; but I fully admit that the mutual relations of organic beings are more important; and as the number of species in any country goes on increasing, the organic conditions of life must become more and more complex.