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Gradually, liowever, there came a natural reaction against this mania for spéculation.
During the last few decades the interest of biologists has been concentrated more and more on
more exact methods of investigation, especially experimental investigation. With the
watch-word „More facts, less theory“ scientists have attacked, with brilliant results, such problems
as the conception of species, variability, heredity, the factors that produce species, etc. Beneath
the pressure of the multitude of facts discovered by scientists during this period a great
deal of the bold speculative fabric of the preceding period has collapsed piece by piece; manv
„pedigrees“ and hypothetical original forms have been proved to be untenable.
As a result of this reverse theoretical classification has been neglected, perhaps even
more tlian it deserved. A number of investigators have even expressed a wish that classification
should quite get rid of the theory of evolution and that it should only have as its aim a good
characterization and a lucid arrangement of the organic world; in other words they desire a
return to the tasks that the classifier formerly looked upon as his.
It is certain that this is going too far. Only after the introduction of the principle of
evolution into classification can the latter be said to have been raised to the level of a science.
To separate these two things would certainly be a retrogressive step. I should like to quote
in this connection a statement of L. PLATE, 1914, p. 109: „Von jeder größeren
systematischen Abhandlung sollte man erwarten, daß sie mit phyletischen Betrachtungen
abschließt und alle zurzeit vorliegenden Beobachtungen aus dem eigenen Untersuchungsgebiet
und aus verwandten Disziplinen (Anatomie, Embryologie) zusammenträgt und nach dieser
Richtung hin prüft“.
In dealing with the theoretical problems connected with evolution it seems to be most
convenient to retain the method of working out hypothetical original forms — a crystallization
of the qualities that are assumed to be original — and „pedigrees“ — graphical presentations
of the hypothetical genetic position of the different systematic units. The argument may gain
considerably in clearness by the use of this method. But a far deeper criticism must be made
than was formerly the case; the hypothèses must be founded on a very broad basis of facta;
it is best to stop when the facts cease to furnish distinct evidence.
I shall attempt below to give an exposition of the natural system and the history of
the evolution of the Ostracods according to the results given by previous writers and
by my own studies of this group of animais.
In ail the works published before 1850 the Ostracods were divided directly into
genera. In this year there appeared \V. Baird’s important work „Natural H ist o ry
of the British Entomostrac a“, in which this group of animais was divided into
three families:
Family I. C y pr id ae with the genera Cypris and Candona
„ II. Cytheridae „ „ „ Cythere „ Cythereis
„ III. Cypridinadae „ „ genus Cypridina.
In J. D. Dana’s large work on the Crustacea collected by the „United States
Exploring Expeditio n“ another important advance is to be noted, as the Ostr
a-c o d s are here divided into two families, both of which are again divided into two sub-families:
llistory oj the
nat-Ural system of the
Ostracods.
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