When a fragment of an organism transforms, under appropriate

conditions, into a typical individual, the process includes
degenerative aa well as regenerative phases
When a fragment of an organism transforms, under appropriate
conditions, into a typical individual, the process includes
degenerative aa well as regenerative phases. There is always
some simplification of the structures present, whose character
and amount is determined by the degree of specialization which
has been attained. The smaller the piece, within certain
limits, and the younger physiologically, the more nearly does
it return to embryonic conditions, a fact which can be studied
admirably in the hydroid Corymorpha. In some cases the
simplification is accomplished by abrupt sacrifice of highly
specialized parts, as in Corymorpha, when in a process of
simplification connected with acclimatization to aquarium
conditions, the large tentacles of well-grown specimens fall
away completely from their bases. In other hydroids (e. g.,
Campanularia) the tentacles may be completely absorbed into the
body of the hydranth from which they originally sprang. Among
tissue cells degenerative changes may be abrupt, as in the
sacrifice of the highly specialized fibrillae in muscle cells;
or they may be very gradual, as in the transformation of cells
of one sort into another that occurs in the regeneration of
tentacles in Tubularia.


semiologic