Paulmeir (1899) describe the diverging bivalent halves of the tetrad as being united each by two fibres with the corresponding spindle pole.
Elasmobranchs), the first during the contraction of the spireme thread, the second during the looping up of the bivalent segments.
For the chromosomes of the heterotype mitosis arise by the looping round, not opening out, of the bivalent chromosomes.
The difficulty is, however, at once overcome if the unripe chromosomes are associated in pairs in the equatorial plate, for the bivalent chromosomes so produced are bipolar just as are the adult (i.
The same fact obtains in the animal kingdom, where Loeb and others have found that the toxicity of solutions of sodium chloride for marine animals is reduced by the introduction of salts of the bivalent metals.
For bivalent metals the atomic weight is equal to the weight of two equivalents, for n-valent metals it is equal to the weight of n equivalents.
Such metals as mercury and copper, which are able to give not one but two bases, are of particular importance for distinguishing univalent and bivalent metals.
And, as we shall afterwards see, magnesium is in many respects closely analogous to zinc, which fact obliges us to regard magnesium as a bivalent metal.
As we shall see in describing them, there are also many analogous metals among the bivalent elements, some of which also give volatile compounds.
Among the bivalent metals the first place, with respect to their distribution in nature, is occupied by magnesium and calcium, just as sodium and potassium stand first amongst the univalent metals.
Bivalent ions are far more efficient than univalent; trivalent, in turn, still more effective than bivalent.
Since thebivalent metal ions are precipitated by sodium carbonate as carbonates and the trivalent ones as hydroxides, the reagent, obviously, cannot be used to separate the two groups.
The members of the aluminium group form hydroxides, which are much weaker bases than are the hydroxides of the bivalent group just considered.
The connection of the element x with the spireme up to the stage where the spireme segments to form the bivalent chromosomes.
Again, one finds a few cases like figure 176, where the spireme is segmented into bivalent chromosomes, each component showing a longitudinal split.
Here we have again a continuous spireme connected with the element x, making it seem improbable that the bivalent chromosomes are really separated in the bouquet stage.
Apparently all of these forms straighten out so that the two components of the bivalent chromosome stand end to end as dumbbells or compressed crosses in the metaphase of the first maturation spindle (figs.
Here the components of the unequal pair are the small spherical chromosome and one of the several chromosomes third in size, forming a comparatively small unsymmetrical bivalent (figs.
Figure 145 is a prophase showing the bivalent chromosomes still connected by linin fibers.
In figure 192 are shown several of the bivalent chromosomes, including the unsymmetrical pair, from nuclear prophases of the first division, all from the same cyst.
In Tenebrio molitor, the unequal pair behaved in every respect like the other bivalent chromosomes.
