Parthenogenetic Sentence Examples
Many species of Thysanoptera are known to be habitually parthenogenetic. The eggs are laid on the food-plant, those females possessed of an ovipositor cutting through the epidermis and placing their eggs singly within the plant-tissues; a single female may take five or six weeks to deposit all her eggs.
The worm inhabits the lung of the frog and toad, and is hermaphrodite (Schneider) or parthenogenetic (Leuckart); the embryos hatched from the eggs find their way through the lungs into the alimentary canal and thence to the exterior; in a few days they develop into a sexual larva, called a Rhabditiform larva, in which the sexes are distinct; the eggs remain within the uterus, and the young when hatched break through its walls and live free in the perivisceral cavity of the mother, devouring the organs of the body until only the outer cuticle is left; this eventually breaks and sets free the young, which are without teeth, and have therefore lost the typical Rhabditis form.
It appears that in parthenogenetic eggs two polar nuclei are formed.
Doncaster (1906-1907) on the eggs of sawflies, the number of chromosomes is not reduced in parthenogenetic egg-nuclei, while, in eggs capable of fertilization, the usual reduction-divisions occur.
Cases of parthenogenetic reproduction, or reproduction without the intervention of the male, have been recorded in the case of two genera (Filistata and Tegenaria), and may be commoner than is usually supposed.Advertisement
The suggestion requires further experimental testing, for which the case of the parthenogenetic production of a portion of the offspring, in such insects as the bee, offers a valuable opportunity for research.
Some authors looking upon these as parthenogenetic ova regard the developmental cycle as one composed of an alternation of parthenogenetic and of sexual generations.
These root-dwelling insects are females, which lay parthenogenetic eggs.
They moult five times, becoming with each change of skin darker in colour; in about three weeks they become adult and capable of laying parthenogenetic eggs.
The views of Adler as to the alternation of generations of numerous gall-flies have been fully confirmed, it having been ascertained by direct observation that the galls and the insects produced from them in one generation are entirely different from the next generation; and it has also been rendered certain that frequently one of the alternate generations is parthenogenetic, no males being produced.Advertisement
Limnadia (Brongniart, 1820) is supposed to consist of species exclusively parthenogenetic. But when asked to believe that males never occur among these amazons, one cannot but remember how hard it is to prove a negative.
In some of the genera parthenogenetic propagation is carried to such an extent that of the familiar Cypris it is said, " until quite lately males in this genus were unknown; and up to the present time no male has been found in the British Islands " (Brady and Norman, 1896).
Claims to have created both cloned and parthenogenetic human embryos in November seem to have been premature.
In certain gall-flies (Cynipidae) no males are known to exist at all, and the species seems to be preserved entirely by successive parthenogenetic generations.
Metchnikoff observed (1866) in the development of the parthenogenetic eggs produced by the precocious larva of the gall-midge Cecidomyia that a large " polar-cell " appeared at one extremity during the primitive cellsegmentation.Advertisement
They always give rise to parthenogenetic females (see Reproduction).