m, and that neither could be solved in isolation
from the other. "The concept of function-change is purely
physiological;" he writes, "it contains the elements out of which
perhaps a history of the evolution of function may gradually arise, and
for this very reason it will be of great utility in morphology, for the
evolutionary history of structure is only the concrete projection of the
content and course of the evolution of function, and cannot be
comprehended apart from it" (p. 70).[402]

It is very instructive in this connection to note that Dohrn was not,
like so many of his contemporaries, a dogmatic materialist, but upheld
the commonsense view that vital phenomena must, in the first instance at
least, be accepted as they are. "It is for the time being irrelevant,"
he writes, "to squabble over the question as to whether life is a result
of physico-chemical processes or an original property (_Urqualitaet_) of
all being.... Let us take it as given" (p. 75).

Semper's speculations on the genetic affinity of Articulates and
Vertebrates are contained in two papers[403] which appeared about the same
time as Dohrn's. He openly acknowledges that his work is essentially a
continuation of Geoffroy's transcendental speculations, and gives in his
second paper a good historical account of the views of his great
predecessor. It is a significant fact that evolutionary morphologists
very generally held that Geoffroy was right in maintaining against
Cuvier[404] the unity of plan of the whole animal kingdom, for they saw in
this a strong argument for the monophyletic descent of all animals from
one common ancestral form.

In his first paper Semper does little more than break ground; he insists
on the fact that both Annelids and Vertebrates are segmented animals,
and he points out how close is the analogy between the nephridia or
"segmental organs" of the former and the excretory (mesonephric) tubules
of the latter, upon which he published in the same volume an extensive
memoir. At this time he considered _Balanoglossus_--by reason of its
gill-slits (its notochord he did not know)--to be the nearest living
representative of the ancestral form of Vertebrates and Annelida.

His second paper is a more exhaustive piece of work and deals with every
aspect of the problem, both from an anatomical and from an embryological
standpoint. It is consciously and admittedly an attempt to apply
Geoffroy's principle of the unity of plan and compos