M Database Inspector (cheetah)
|Not logged in. Login|
|12 - Geographical Distribution -- continued||12-40 - On the relations of the inhabitants of islands to those of the nearest mainland||10||
Besides the absence of terrestrial mammals in relation to the remoteness of islands from continents, there is also a relation, to a certain extent independent of distance, between the depth of the sea separating an island from the neighbouring mainland, and the presence in both of the same mammiferous species or of allied species in a more or less modified condition.
Mr. Windsor Earl has made some striking observations on this head in regard to the great Malay Archipelago, which is traversed near Celebes by a space of deep ocean; and this space separates two widely distinct mammalian faunas.
On either side the islands are situated on moderately deep submarine banks, and they are inhabited by closely allied or identical quadrupeds.
No doubt some few anomalies occur in this great archipelago, and there is much difficulty in forming a judgment in some cases owing to the probable naturalisation of certain mammals through man's agency; but we shall soon have much light thrown on the natural history of this archipelago by the admirable zeal and researches of Mr Wallace.
|01 - Variations Under Domestication||01-08 - Breeds of the Domestic Pigeons, their Differences and Origin||10||
Believing that it is always best to study some special group, I have, after deliberation, taken up domestic pigeons.
I have kept every breed which I could purchase or obtain, and have been most kindly favoured with skins from several quarters of the world, more especially by the Hon. W. Elliot from India, and by the Hon. C. Murray from Persia.
Many treatises in different languages have been published on pigeons, and some of them are very important, as being of considerable antiquity.
I have associated with several eminent fanciers, and have been permitted to join two of the London Pigeon Clubs.
The diversity of the breeds is something astonishing.
Compare the English carrier and the short-faced tumbler, and see the wonderful difference in their beaks, entailing corresponding differences in their skulls.
The carrier, more especially the male bird, is also remarkable from the wonderful development of the carunculated skin about the head; and this is accompanied by greatly elongated eyelids, very large external orifices to the nostrils, and a wide gape of mouth.
The short-faced tumbler has a beak in outline almost like that of a finch; and the common tumbler has the singular inherited habit of flying at a great height in a compact flock, and tumbling in the air head over heels.
The runt is a bird of great size, with long massive beak and large feet; some of the sub-breeds of runts have very long necks, others very long wings and tails, others singularly short tails.
The barb is allied to the carrier, but, instead of a long beak has a very short and broad one.
The pouter has a much elongated body, wings, and legs; and its enormously developed crop, which it glories in inflating, may well excite astonishment and even laughter.
The turbit has a short and conical beak, with a line of reversed feathers down the breast; and it has the habit of continually expanding slightly, the upper part of the oesophagus. The Jacobin has the feathers so much reversed along the back of the neck that they form a hood; and it has, proportionally to its size, elongated wing and tail feathers.
The trumpeter and laugher, as their names express, utter a very different coo from the other breeds.
The fantail has thirty or even forty tailfeathers, instead of twelve or fourteen- the normal number in all the members of the great pigeon family: these feathers are kept expanded, and are carried so erect, that in good birds the head and tail touch: the oil-gland is quite aborted.
Several other less distinct breeds might be specified.
|03 - Struggle for Existence||03-01 - Bears on Natural Selection||10||
BEFORE entering on the subject of this chapter, I must make a few preliminary remarks, to show how the struggle for existence bears on Natural Selection.
It has been seen in the last chapter that amongst organic beings in a state of nature there is some individual variability: indeed I am not aware that this has ever been disputed.
It is immaterial for us whether a multitude of doubtful forms be alled species or sub-species or varieties; what rank, for instance, the two or three hundred doubtful forms of British plants are entitled to hold, if the existence of any well-marked varieties be admitted.
But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. How have all those exquisite adaptations of one part of the organisation to another part, and to the conditions of life, and of one organic being to another being, been perfected?
We see these beautiful co-adaptations most plainly in the woodpecker and the mistletoe; and only a little less plainly in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird; in the structure of the beetle which dives through the water; in the plumed seed which is wafted by the gentlest breeze; in short, we see beautiful adaptations everywhere and in every part of the organic world.
|02 - Variations Under Nature||02-01 - Variability||10||
BEFORE applying the principles arrived at in the last chapter to organic beings in a state of nature, we must briefly discuss whether these latter are subject to any variation.
To treat this subject properly, a long catalogue of dry facts ought to be given; but these shall reserve for a future work.
Nor shall I here discuss the various definitions which have been given of the term species.
No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.
Generally the term includes the unknown element of a distant act of creation. The term "variety" is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved.
We have also what are called monstrosities; but they graduate into varieties.
By a monstrosity I presume is meant some considerable deviation of structure, generally injurious, or not useful to the species.
Some authors use the term "variation" in a technical sense, as implying a modification directly due to the physical conditions of life; and "variations" in this sense are supposed not to be inherited; but who can say that the dwarfed condition of shells in the brackish waters of the Baltic, or dwarfed plants on Alpine summits, or the thicker fur of an animal from far northwards, would not in some cases be inherited for at least a few generations?
And in this case I presume that the form would be called a variety.