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But I had to point out then that no case was known of "parthenogenesis" that is to say, reproduction by unfertilised eggs among the whole series of vertebrate animals, the fishes, amphibians, reptiles, birds, and mammals.
Other moths bred by collectors behaved in the same way, but the grubs were reared to maturity, and three successive generations of "fatherless" moths were obtained. In these cases the hatching of unfertilised eggs is not known to occur in a state of nature, although it probably occurs occasionally.
Some few moths and flies also reproduce naturally during summer by unfertilised eggs, and the brine-shrimps and some other fresh-water shrimps produce "fatherless" broods from their eggs, sometimes for years in succession, until "one fine day" some males are hatched, owing to what causes we do not know.
The queen bee naturally and regularly lays a certain number of unfertilised eggs, and these produce, not females as do the unfertilised eggs of plant-lice, etc., but male bees the drones and it is only from such eggs that the drones of bees are born. These are the chief cases of regular and natural parthenogenesis, but there are others which might be enumerated.
It happened, unfortunately for Brighteye, that, while the construction of the "redd" was in progress, some of the eggs unfertilised and therefore not heavy enough to sink to the bottom of the water were borne slowly by the current to the ford below the pool, just as the shrew was occupied there in vain attempts to teach the vole how to hunt for insects among the pebbles.
The plant-lice "naturally" reproduce through the summer by unfertilised eggs producing only females, but in the first cold of autumn males are hatched from some of the eggs, and the eggs of this generation are fertilised and bide through the winter, hatching in the following spring.
Wilson points out that in the bee, where fertilised eggs develop into females and unfertilised into males, we should have to assume that the X chromosome in the female gamete is a female determiner which meets a recessive male determiner in the X chromosomes of the sperm. Dr.
This investigator found that there were 48 chromosomes in the female cell, 47 in the male; after the reduction divisions the unfertilised ova had 24 chromosomes, half the spermatids 24 and half 23, so that sex is determined in man by the spermatozoon. We may mention a few other in animals, referring the reader for a fuller account to the works cited.
The soma with its male and female somatic characters has nothing to do with the question, since somatic sex-differences may be altogether wanting, and moreover, the essential male character, the formation of spermatozoa, is by the Mendelian hypothesis due to descent of the male gametes from the original fertilised or unfertilised ovum.
The Ranger never paused from the time he set out until he found himself under a portion of the long brick-wall that still divides the richly ornamented park from the arid and unfertilised heath.
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