| → in its natural or primary progress. 1866 |
| performed in a primary and gradual manner. 1869 1872 |
|
| ↑ 4 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| Many insects, and especially certain crustaceans, show us what wonderful changes of structure can be effected during development.
Such changes, however, reach their climax in the so-called alternate generations of some of the lower animals.
It is, for instance, an astonishing fact that a delicate branching coralline, studded with polypi and attached to a submarine rock, should produce, first by budding and then by transverse division, a host of huge floating jelly-fishes; and that these should produce eggs, from which are hatched swimming animalcules, which attach themselves to rocks and become developed into branching corallines; and so on in an endless cycle.
The belief in the essential identity of the process of alternate generation and of ordinary metamorphosis has been greatly strengthened by Wagner's discovery of the larva or maggot of a fly, namely the Cecidomyia, producing asexually other larvæ, and these others, which finally are developed into mature males and females, propagating their kind in the ordinary manner by eggs.
|
|
| → What great 1866 |
| Many insects, and especially certain crustaceans, show us what wonderful 1869 |
|
| → When, however, we read of the several wonderful cases, recently discovered, of 1866 |
| Such changes, however, reach their climax in 1869 |
|
| → animals, we come to the climax of developmental transformation. 1866 |
| some of the lower animals. 1869 |
|
| → What fact can be more astonishing than 1866 |
| It is, for instance, an astonishing fact 1869 |
|
| → This view 1866 |
| The belief in the essential identity 1869 |
|
| → close connection between 1866 |
| process of 1869 |
|
| → of a Cecidomyia,— that is of the 1866 |
| or 1869 |
|
| → fly,— 1866 |
| fly, namely the Cecidomyia, 1869 |
|
| → within its body 1866 |
| OMIT 1869 |
|
| ↑ 5 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| It may be worth notice that when Wagner's remarkable discovery was first announced, I was asked how was it possible to account for the larvæ of this fly having acquired the power of asexual reproduction.
As long as the case remained unique no answer could be given.
But already Grimm has shown that another fly, a Chironomus, reproduces itself in nearly the same manner, and he believes that this occurs frequently in the Order.
It is the pupa, and not the larva, of the Chironomus which has this power; and Grimm further shows that this case, to a certain extent, "unites that of the Cecidomyia with the parthenogenesis of the Coccidæ;"— the term parthenogenesis implying that the mature females of the Coccidæ are capable of producing fertile eggs without the concourse of the male.
Certain animals belonging to several classes are now known to have the power of ordinary reproduction at an unusually early age; and we have only to accelerate parthenogenetic reproduction by gradual steps to an earlier and earlier age,— Chironomus showing us an almost exactly intermediate stage, viz., that of the pupa— and we can perhaps account for the marvellous case of the Cecidomyia.
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| ←Subtitle not present 1866 1869 1872
Embryology
.— 1859 1860 1861 |
| → remarked that various parts and organs of the same individual animal are during an early embryonic period exactly like each other, but become 1866 |
| casually remarked that certain organs 1859 1860 1861 |
| stated that various parts and organs 1869 |
| stated that various parts 1872 |
|
| → adult state widely different and serve for widely different purposes. 1866 |
| individual, which when mature become widely different and serve for different purposes, are in the embryo exactly alike. 1859 1860 1861 |
| same individual are exactly like each other during an early embryonic period, but in the adult state become widely different and serve for widely different purposes. 1869 |
| same individual which are exactly alike during an early embryonic period, become widely different and serve for widely different purposes in the adult state. 1872 |
|
| → distinct species and genera within 1866 |
| the most distinct species within 1869 |
| the most distinct species belonging to 1872 |
|
