Azolla has roots depending from the lower surface of the stem into the water, while these organs are completely wanting in Salvinia, their place being taken functionally by highly divided leaves borne on the ventral surface of the stem.
That for the tongue, with which the other points are functionally connected.
Each neuron or nerve cell is a morphologically distinct and discrete unit connected functionally but not structurally with its neighbours, and leading its own life independently of the destiny of its neighbours.
The innumerable cases of structures, which are rudimentary and apparently useless, in species, the close allies of which possess well-developed and functionally important homologous structures, are readily intelligible on the theory of evolution, while it is hard to conceive their raison.
The dentition of the kangaroos, functionally considered, thus consists of sharp-edged incisors, most developed near the median line of the mouth, for the purpose of cropping herbage, and ridged or tuberculated molars for crushing.
As a result of these various degenerations the functions of the body deteriorate, the faculties become blunted, and the muscular energy of the body is below what it was in earlier life, while the secreting glands in certain instances become functionally obsolescent.
In accordance with the prevalent antithetic view of the alternation of generations in these plants (see PLANTS, REPRODUCTION or), the forms distinguished as sporophyte and gametophyte are not homogenetic; consequently their leaves are not homologous, but are only functionally similar (homoplastic; see infra).