INTRODUCTION Z07 
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or less accuracy in any text-book of zoology,! and it is enough to remark 
that by the naturalist just named Birds and Reptiles have been brigaded 
together under the name of Sauropsida as forming one of the three 
primary divisions of the Vertebrata—the other two being Ichthyopsida and 
Mammalia. Yet Birds have a right to be considered a Class, and as a 
Class they have become so wholly differentiated from every other group 
of the Animal Kingdom that, among recent and even the comparatively 
few fossil forms known to us, there is not one about the assignation of 
which any doubt ought now to exist, though some naturalists have 
refused a place among Aves to Archxopteryx, of which, as elsewhere stated 
(pages. 278-280), the remains of only two individuals—most probably 
belonging to as many distinct forms ?—have been discovered. Yet one of 
them was referred, without much hesitation, by Vogt to the Class Reptilia 
on grounds which seem to be mistaken, since it was evidently in great 
part if not entirely clothed with feathers,’ and scarcely any one now 
doubts that its Bird-like characters predominate over those which are 
obviously Reptilian, while most authorities leave the genus as the sole 
representative as yet known of the Subclass SauruR«, established for its 
reception by Pref. Hackel. The great use of the discovery of Archexopterysx 
to naturalists in general was the convincing testimony it afforded as to 
what is well called “the imperfection of the Geological Record.” To 
ornithologists in particular its chief attraction is the evidence it furnishes 
in proof of the evolution of Birds from Reptiles ; though, as to the group 
of the latter from which the former may have sprung, it tells us little 
that is not negative. It throws, for instance, the Pterodactyls #—so often 
imagined to be nearly related to Birds, if not to be their direct ancestors 
—completely out of the line of descent. Next to this its principal 
1 The various schemes for classifying Birds set forth by the authors of general 
text-books of Zoology do not call for any particular review here, as almost without 
exception they are so drawn up as to be rather of the nature of a compromise than 
of a harmony. The best and most notable is that by Prof. Carus in 1868 (tom. 
cit. i. pp. 191-368); but it is of course now antiquated. Among the worst 
schemes is that by Prof. Claus in 1882 (Grundziige der Zoologie, ii. pp. 818-388) ; but 
Dr. R. Hertwig’s Lehrbuch der Zoologie (Jena: 1892, pp. 588-544) is quite as bad. Of 
most other similar text-hooks that have come under my notice, the less said the better. 
2 See Prof. Seeley’s remarks on the differences between the two specimens (Geol. 
Mag. 1881, p. 454). 
3 Vogt laid much stress on the absence of feathers from certain parts of the body 
of the second example of Archxopteryx now, thanks to Dr. Werner Siemens, in the 
museum of Berlin. But Vogt himself shewed that the parts of the body devoid of 
feathers are also devoid of skin. Now it is well known that among most existing 
Birds the ordinary “ contour-feathers ” have their origin no deeper than the skin, and 
thus if that decayed and were washed away the feathers growing upon it would 
equaily be lost. This has evidently happened (to judge from photographs) to the 
Berlin specimen just as to that which is in London. In each case, as Owen rightly 
suggested of the latter, the remains exactly call to mind the very familiar relics of 
Birds found on a seashore, exposed perhaps for weeks or even months to the wash of 
the tides so as to lose all but the deeply-seated feathers, and finally to be embedded 
in the soft soil. Vogt’s paper is in the Revue Scientifique, ser. 2, ix. p. 241, and an 
English translation of it in The bis for 1880, p. 434. 
4 In 1866 Owen (Anatomy of Vertebrates, ii. p. 18) maintained that ‘‘ Derivatively 
the class of Birds is most closely connected with the Pterosawrian order,” i.e. the 
Pterodactyls ; and the view is probably still held by many persous. 
