Here, then, we leave the lower forms of Metazoa in their condition of permanent gastrulæ.
In general, however symbiosis is rarer in the Metazoa than in the metaphyta.
I will now pass on to consider the embryogeny of the Metazoa, beginning at its earliest stage in the fertilization of the ovum.
Minot had tried to prove that the death of Metazoa is due to the greater differentiation and specialization of their tissues.
And its marvellous development in the Metazoa appears ultimately to depend upon the highly specialized character of germ-cells.
There are but few groups of the Metazoa which are not provided with optic organs of greater or less complexity.
The whole of the animals with bodies composed of definite tissues of this kind are known as the Metazoa.
But among the Metazoa we find this form of individuality only in the lower (and generally stationary) stages of development.
The reproduction of the forms above the Protozoa, which are known as the Metazoa, takes place by two methods, viz.
Parasitism in the Metazoa (in all groups) is even more frequent and interesting than in the metaphyta.
Metazoa Met·a·zo·a (mět'ə-zō'ə)
A subdivision of the animal kingdom that includes all multicellular animal organisms having cells that are differentiated and form tissues and organs.