The m-chromosomes have here formed a precocioustetrad (m).
In the cubic system, for example, the three crystallographic axes are taken parallel to the three tetrad axes of symmetry, i.
In this class there is no centre of symmetry nor cubic planes of symmetry; the three tetrad axes become dyad axes of symmetry, and the four triad axes are polar, i.
There are five axes of symmetry, one tetrad and two pairs of dyad, each perpendicular to a plane of symmetry.
The elements of symmetry are a tetrad axis with a plane perpendicular to it, and a centre of symmetry.
On a cube, for example, there are three zones each containing four faces, the zone-axes being coincident with the three tetrad axes of symmetry.
Thus, by rotation about the vertical tetrad axis a3a'3 the four upper faces are obtained; and by rotation of these about one or other of the horizontal tetrad axes the eight faces are derived.
Here the only element of symmetry is the tetrad axis.
Here there are two pairs of vertical planes of symmetry intersecting in the tetrad axis.
They are parallel to the edges of the cube, and in the different classes coincide either with tetrad or dyad axes of symmetry.
Such an axis of symmetry is known as a tetrad axis of symmetry.
The unequal axis is spoken of as the principal axis or morphological axis of the crystal, and it is always placed in a vertical position; in five of the seven classes of this system it coincides with the single tetrad axis of symmetry.
Other tetrad axes of the octahedron are a2a'2 and a1a1.
The segments have begun to open out at the center to give the cross which is the typical tetrad form in Stenopelmatus.
Chromosome in single diamond or tetrad form, as they usually come into the spindle.
In other cases the split persists as in figure 110 and leads to the formation of crosses of a tetrad character (figs.
Prophase of first maturation mitosis, showing the unsymmetrical pair and the tetrad nature of the symmetrical pairs.
The tetrad expresses the first mathematical power.
He at once treats the Tetrad as such a leader named "Kolarbasus," and after dealing (vi.
Spores Each a single cell like the preceding, but here only one tetrad in a sporangium ripens, so that each contains only four spores.
Spores" of Seedlike Structure Out of a tetrad in each sporangium only one spore ripens, S in figure, the others, s, abort.
S, large spore within the sporangium wall w; s, the three aborted spores of the tetrad to which S belongs.
That the tetrad should be considered to be thus complete, reminds one of the four elements, the physical and the chemical, the four continents, &c.
