Thus, though he regards the male pronucleus as a product of impregnation, he does not believe it to be the head of a spermatozoon.
Each spermatozoon forms a separatepronucleus with a surrounding sun; and several male pronuclei usually fuse with the female pronucleus.
Ovum of Asterias glacialis, with male and femalepronucleus and a radial striation of the protoplasm around the former.
Thus in Hirudinea, Mollusca, and Nematodes impregnation normally takes place before the formation of the polar bodies is completed, and the male pronucleus is accordingly as large as the female.
The junction of the male and female pronucleus is described by Fol and Selenka in nearly the same manner.
Ovum of Asterias glacialis, after the coalescence of the male and female pronucleus (copied from Fol).
In Echinus, on the other hand, where the polar bodies are formed in the ovary, the malepronucleus is always small.
Each male pronucleus appears to exercise a repulsive influence on other male pronuclei, but to be attracted by the female pronucleus.
Appearance of radial striae round the male pronucleus which gradually travels towards the female pronucleus.
Ovum of Asterias glacialis with the two polar bodies and the female pronucleus surrounded by radial striae, as seen in the living egg (copied from Fol).
When it finally unites with the female pronucleus it is equal in size to the latter.
Three successive stages in the coalescence of the male and female pronucleus in Asterias glacialis.
The discovery of Hertwig as to the formation of the male pronucleus throws a flood of light upon impregnation.
Transportation of the female pronucleustowards the centre of the egg.
Selenka, who has investigated the formation of the male pronucleus in Toxopneustes variegatus, differs in certain points from Fol.
The immediate result of the fusion of the male and female pronucleus is the segmentation or division of the ovum usually into two, four, eight, etc.
In the case when the impregnation is deferred for four hours the male pronucleus never becomes so large as the female pronucleus.
Each spermatozoon forms a separatepronucleus with a surrounding star; and several male pronuclei usually fuse with the female pronucleus.
Thus in Hirudinea, Mollusca, and Nematoidea impregnation normally takes place before the formation of the polar bodies is completed, and the male pronucleus is accordingly as large as the female.
The head of the spermatozoon when in the egg forms a nucleus, for which the name male pronucleusmay be conveniently adopted.
The pronucleus unites permanently with the pronucleus of the ovum, and together they form the Cleavage or Segmentation Nucleus of the fertilized ovum.
It will be objected that four loops cannot be necessary for nuclear division in Ascaris, since such division takes place in the formation of the polar bodies, resulting in the appearance of the female pronucleus with only two loops.
The male pronucleus has the remains of the body of the spermatozoön adhering to it.
The second polar body has just been extruded; both male and female pronuclei contain two chromatin particles; those of the male pronucleus are becoming transformed into a skein.
Only the female pronucleus is shown in this figure.
He finds that in the formation of this cross the female pronucleus takes no part in the development of the zygotic cell, but that when the male pronucleus enters, the female pronucleus is pushed aside and degenerates.
The tail by which it has been moving is cast off, and the head containing the chromosomes and the centrosome enters the egg, forming what is called the male pronucleus (Figs.
This accounts for the fact, which has been often observed, that the female pronucleus is not surrounded by protoplasmic radiations, whereas such radiations are present round the male pronucleus in its approach to the female.
Giard suggests that in some cases of apparently normal fertilization one of the pronuclei may degenerate, the resultant embryo being the product of one pronucleus only.
The general rule appears to be that the female pronucleus is without a centrosome, and that no centrosome appears in the female in the divisions by which the gamete arises from the progamete.
It is the latter alone that combines in conception with the invading nucleus of the fertilising spermatozoon (the pronucleus masculinus).
Part of it is extruded, and part dissolved in the cell contents; only a very small part of it is left to form the basis of a fresh nucleus, the pronucleus femininus.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "pronucleus" in a variety of sentences. We hope that you will now be able to make sentences using this word.
