raca, similar to those which flourished in Cambrian and
Silurian times.

The contributions of palaeontology to the solution of the problems of
descent posed by morphology are, however, not all of this negative
character. The law of recapitulation is in some well-controlled cases
triumphantly vindicated by palaeontology. Thus Hyatt and others found
that in Ammonites the first formed coils of the shell often reproduce
the characters belonging to types known to be ancestral, and what is
more they have demonstrated the actual occurrence of the phenomenon
known as acceleration or tachygenesis, often postulated by speculative
morphologists.[546] This is the tendency universally shown by embryos to
reproduce the characters of their ancestors at earlier and earlier
stages in their development.

The most valuable contribution made by palaeontologists to morphology and
to the theory of evolution arose out of the careful and methodical study
of the actual succession of fossil forms as exemplified in limited but
richly represented groups. Classical examples were the researches of
Hilgendorf[547] on the evolution of _Planorbis multiformis_ in the
lacustrine deposits of Steinheim, those of Waagen[548] on the phylogeny of
_Ammonites subradiatus_, and the work of Neumayr and Paul[549] on
_Paludina_ (_Vivipara_).

These investigations demonstrated that it was possible to follow out
step by step in superjacent strata the actual evolution of fossil
species and to establish the actual "phyletic series."

To take an example from among the Vertebrates, Deperet has shown (_loc.
cit._, pp. 184-9), that the European Proboscidea, belonging to the three
different types of the Elephants, Mastodons and Dinotheria, have evolved
since the Oligocene epoch along five distinct but continuous lines. The
Dinotherian stock is represented at the beginning of the Miocene by the
relatively small form _D. cuvieri_; this changes progressively
throughout Miocene times into _D. laevius_, _D. giganteum_, and _D.
gigantissimum_. Among the Mastodons two quite distinct phyletic series
can be distinguished, the first commencing with _Palaeomastodon
beadnelli_ of the Oligocene, and evolving between the Miocene and
Pliocene into _Mastodon arvernensis_, after traversing the forms _M.
angustidens_ and _M. longirostris_, the second starting with the _M.
turicensis_ of the Lower Miocene and evolving through _M. borsoni_ into
the _M. americanus_ of the Quaternary. The ph