In the first place, we do not know whether parthenogenesis may not finally settle down into completeasexual reproduction.
The conclusion seems inevitable that metagenesis has here proceeded from metamorphosis; that is to say, one stage of the ontogeny, by acquiring asexual propagation, has changed the originally existing metamorphosis into metagenesis.
When the latter is combined with asexual reproduction, as is especially the case with the Hydrozoa, metagenesis may be derived therefrom.
A peculiar larva of certain trematodes which produces cercariæ by asexual reproduction.
After asexual multiplication has gone on for some time, sexual forms become developed.
All of the above means of propagation are asexual and are of importance in our problem of plant breeding.
These simplest forms multiply or reproduce by fission, but such asexual reproduction is almost entirely confined to the unicellular forms of life.
This is an asexual process, and from it results the repetition or reproduction of the form of the original being from which the bulb proceeds.
The cases of asexual perpetuation are by no means so common as the cases of sexual perpetuation; and they are by no means so common in the animal as in the vegetable world.
These are all cases ofasexual multiplication, and there are other instances, and still more extraordinary ones, in which this process takes place naturally, in a more hidden, a more recondite kind of way.
The method of the perpetuation of organic beings is of two kinds,--the asexual and the sexual.
Asexual reproduction, reproduction by division of the cell or body.
The Simple or Asexual Method of Reproduction Materials.
Frequently also the mother or father visit the child before going to sleep, lean over the bed, allow themselves often to press the child passionately to themselves and count this asexual love toward the child.
The plainly erotic character is never wanting in an apparently asexual action, if we penetrate it more deeply.
It is now clear that the apparently asexual desire for fame does not lack its erotic foundation.
Finally it is only among the aquatic forms, and among them only in the families Aeolosomatidae and Naididae, that asexual reproduction by budding takes place.
While asexualgeneration is general, the reproductive organs are more commonly found than in Aeolosoma, though there are still many hiatus in our knowledge of the same in certain genera.
On the Asexual Reproduction of Cecydomyide Larvæ, translated in 'Annals and Mag.
It is satisfactory to find that sexual and asexual generation, by both of which widely different processes the same living creature is habitually produced, are fundamentally the same.
Another difficulty may be here noticed; we have seen that {396} there is an important difference in the frequency, though not in the nature, of the variations in plants propagated by sexual and asexual generation.
The union of the two sexual elements seems to make a broad distinction between sexual and asexual reproduction.
But during the act of asexual production or subsequently to it, they often advance in organisation, as we see in the many cases of "alternate generation.
The latter alone possess the power of producing a new colony, and this takes place by the asexual and sexual methods alternately: in the latter a typical fertilization of large egg-cells by small spermatozoa occurs.
Let us imagine, for the sake of argument, that sexual reproduction had not been introduced into the animal kingdom, and that asexual reproduction had hitherto existed alone.
There are therefore two reasons which lead us to expect that organs which are no longer used will remain unreduced in species with asexual reproduction: first, because only a very slight degree of hereditary variability can be present, viz.
From the fact of its general occurrence, the conclusion is, however, drawn that asexual reproduction could not persist indefinitely as the only mode of reproduction in any species of animal.
But such a result is quite unattainable with the asexual method of reproduction: in other words, natural selection, in the true meaning of the term, viz.
These colonies are propagated by the sexual andasexual (Fig.
The total life-energy, so to speak, is increased, a gain which is not produced by asexual reproduction or by the union of sexual cells of plants which have lived under the same or only slightly different conditions.
As in the asexual reproduction of algae quantitative alteration in the amount of moisture, light, temperature, etc.
Some of these forms remain wingless, while others may develop wings, upon which a wider dispersal of the species depends, but in both cases such females are asexual and viviparous.
The sexual method has for its results an increase of the number of kinds of individual or organism, whereas the asexual affords an increase in the number of individuals of the same kind.
If the asexual method of reproduction alone existed, there would, so far as our knowledge at present extends, be no increase in the number of kinds of organism: no new individuality could arise.
Marchal (1904) on the asexual increase by fission of the early embryos of certain parasitic Hymenoptera (so called germinogony), a phenomenon which had been long ago shown to occur in Lumbricus trapezoides by N.
An asexualplant is one, which, without all the intermediate organs of the stem, at once represents the capsule or ovary.
The asexual plants are simply formations of the tissues, of the galvanic vesicle, and are thus of a female nature.
It may be said, that the asexual plant is naught but seed, and that the seed of the higher plants is a fungus upon a leafy peduncle, a fungus more highly organized by light.
The life of the asexual plants consists simply in the galvanic process.
The most inferior or asexual plants have only seeds devoid of capsule and corolla, and produced without the concurrence of female and male parts.
The asexual are female plants, and are consequently the first or lowest.
The flowerless or asexual plants can have no genuine seed or no embryo.
The Tissue-plants can therefore have no sexual organs; and plants divide accordingly into asexual and sexual plants.
The asexual plants are not cryptogamic, but agamic.
The farinaceous or granular matter, lying next to the germ when within the shell of the true seeds, is called the albumen or perisperm; the seeds of the asexual plants are therefore nothing else but albumen.
As again the true seed is a leaf-formation, and possesses therefore cotyledons or seed-lobes, such seeds must be wanting in the asexual plants; they are therefore Acotyledones.
The asexual spores, which are not motile, are formed in some of the surface cells of the thallus.
Lastly, it is interesting to note that the asexual spores, the male cells, and the female cells are generally produced on different plants of the same species.
In the rhodosperms the reproduction may be either asexual or sexual.
As with the last division, the reproduction of the melanospores may be asexual or sexual.
In all of her lowest plants and animals she uses theasexual method of reproduction.
This sort of reproduction, in which a piece of the old parent grows up into the new generation, is called the asexual method.
And--for the sake of clearness--what I am concerned to show is that a woman is not necessarily asexual or cold because she will not use an appeal to sexuality in order to get what she wants.
It is the asexualwhich is the lower, and the sexually differentiated which is the higher organism.
But it is still not understood that the woman who is not temperamentally asexual may easily be made so by being forced when she is not ready, and physically hurt when a little patience and tenderness would have saved her.
But as we pass from the lower to the higher, we pass from the less individual to the more individual; from asexual to sexual.
When the tail completely atrophies the larva leaves its transparent covering, and becomes anasexual Doliolum with a dorsal stolon.
Although the stolon arises while the asexual Salp is still in an embryonic condition, it does not become fully developed till long after the asexual Salp has attained maturity.
The ovum gives rise, as already described, to a tailed embryo which subsequently develops into a cask-shaped asexual form.
The solitaryasexual Salp clearly corresponds with the Cyathozooid of Pyrosoma, though it has not, like the Cyathozooid, undergone a retrogressive metamorphosis.
This stolon is simply the stalk by which each median bud was primitively attached to the stolon of the first asexual form.
The asexual Salp, the embryonic development of which has just been described, may be compared to the Cyathozooid of Pyrosoma, from which it mainly differs in being fully developed.
This stolon is divided into a series of lateral buds after the solitary asexual Salp has begun to lead an independent existence.
Budding, the second, and perhaps the most usual mode of asexual propagation, may be said to mark a further step in the development of the reproductive process.
The feature common to all ordinary forms of asexual multiplication is that the reproductive process is independent of sex; what starts the new life is the half, or a liberated portion of the single parent cell.
It is probable that these three stages of asexual reproduction are not all the steps actually taken by Nature in the development of the early life-process.
Differing from the sponges and the polyps and jellyfishes, the reproduction of the Echinoderms is always sexual; young or new individuals are never produced by budding, or in any other asexual way.
In one view they are mere asexual conidia, and the term pycnoconidia is accordingly applied since they are borne in structures like the non-sexual pycnidia of other fungi.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "asexual" in a variety of sentences. We hope that you will now be able to make sentences using this word.
