the organs which disappear
during the development of the individual animal" (p. 73,
1808).

[376] _The History of Creation_, vol. i., p. 310, 1876.
Translation of the _Natuerliche
Schoepfungsgeschichte_, 1868.

[377] _Cf._ a parallel passage from Serres, _supra_, p.
82.

[378] _Jenaische Zeitschrift_, ix., pp. 402-508, 1875.

[379] _Loc. cit._, ix., p. 409.

[380] _Untersuchungen zur vergl. Anatomie d.
Wirbelthiere_, Leipzig, i., 1864; ii., 1865; and iii.,
1872.

[381] "U. d. Biologie in Jena waehrend des 19
Jahrhunderts," _Jenaische Zeitschrift_, xxxix., pp.
713-26, 1905.

[382] _Grundriss der vergl. Anatomie_, 1874, 2nd ed.,
1878. Trans. by F. Jeffrey Bell, revised by E. Ray
Lankester, as _Elements of Comparative Anatomy_, London,
1878.

[383] "This theory (evolution) shows that what was
formerly called 'structural plan' or 'type' is the sum
of the dispositions (_Einrichtungen_) of the animal
organisation which are perpetuated by heredity, while it
explains the modifications of these dispositions as
adaptive states. Heredity and adaptation are thus the
two important factors through which both the unity and
the variety of organisation can be understood"
(_Grundzuege_, p. 19).

[384] _History of Creation_, i., pp. 241-2.

[385] "On the use of the term Homology in Modern Zoology,
and the distinction between Homogenetic and Homoplastic
agreements," _Ann. Mag. Nat. Hist._ (4), vi., pp. 35-43,
1870.

CHAPTER XV

EARLY THEORIES ON THE ORIGIN OF VERTEBRATES

Haeckel and Gegenbaur set the fashion for phylogenetic speculation, and
up to the middle 'eighties, when the voice of the sceptics began to make
itself heard, the chief concern of the younger morphologists was the
construction of genealogical trees. The period from about 1865 to 1885
might well be called the second speculative or transcendental period of
morphology, differing only from the first period of transcendentalism by
the greater bulk of its positive achievement. It must be remembered that
the later workers (at least towards the end of this period) had immense
advantages over their predecessors in the matter of equipment and
technique; they possessed well-fitted laboratories in the university
towns and by the sea; they had at their command perfected microscopes
and microtomes; while the whole new techniq