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It is determined by a cause; and, as this cause acts invariably, the same arrangement must be reproduced if I renew the experiment. I renewed it, therefore, in the years that followed, with as many appliances as I could find bramble-stumps; and, at each new test, I saw once more what I had seen with such interest on the first occasion.
Sometimes, again, a grub dies in its cocoon; and the cradle of the deceased, now turned into a coffin, forms an everlasting obstacle. How shall the insect cope with such grave circumstances? Among the many bramble-stumps which I have collected, some few have presented a remarkable peculiarity.
When we have no glass houses at our disposal, we can see these little architectural refinements in the reeds of the hurdles, if we open them at the right season. By splitting the bramble-stumps in the course of July, we perceive also that the Three-pronged Osmia, notwithstanding her narrow gallery, follows the same practice as Latreille's Osmia, with a difference.
The usual door being inaccessible, a side-window had been opened by means of the insect's jaws. The cocoons, torn, but still in position in the lower rooms, left no doubt as to this eccentric mode of exit. The same fact, moreover, was repeated, in several bramble-stumps, in the case of Osmia tridentata; it was likewise repeated in the case of Anthidium scapulare.
Among the number are the different inhabitants of the bramble-stumps, notably the Three-pronged Osmiae, who form an excellent subject for observation, partly because they are of imposing size bigger than any other bramble-dwellers in my neighbourhood partly because they are so plentiful. Let us briefly recall the Osmia's habits.
Among the number are the different inhabitants of the bramble-stumps, notably the Three-pronged Osmiae, who form an excellent subject for observation, partly because they are of imposing-size bigger than any other bramble-dwellers in my neighbourhood partly because they are so plentiful. Let us briefly recall the Osmia's habits.
When we have no glass houses at our disposal, we can see these little architectural refinements in the reeds of the hurdles, if we open them at the right season. By splitting the bramble-stumps in the course of July, we perceive also that the Three-pronged Osmia notwithstanding her narrow gallery, follows the same practice as Latreille's Osmia, with a difference.
If the famous law of natural selection, which is said to govern and transform the world, had any sure foundation; if really the fittest removed the less fit from the scene; if the future were to the strongest, to the most industrious, surely the race of Osmiae, which has been perforating bramble-stumps for ages, should by this time have allowed its weaker members, who go on obstinately using the common outlet, to die out and should have replaced them, down to the very last one, by the stalwart drillers of side-openings.
It was easy to repeat the experiment without changing anything in the natural conditions, except the direction of the cocoons: all that I had to do was to hang up some bramble-stumps as I found them, vertically, but with the opening downwards. Out of two stalks thus arranged and peopled with Osmiae, not one of the insects succeeded in emerging.
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