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The law of geographical relationship above alluded to, between the living vertebrata of every great zoological province and the fossils of the period immediately antecedent, even where the fossil species are extinct, is by no means confined to the mammalia.
As this great geologic change slowly advanced through its long history of earthquakes, volcanic disturbances, minor upheavals and subsidences as the extent of the archipelago became greater and its smaller islands coalesced into larger ones, while its coast-line grew still longer and more varied, and the neighbouring sea more thickly inhabited by inferior forms of life; the lowest division of the vertebrata would begin to be represented.
In the higher Vertebrata the branchiæ have wholly disappeared the slits on the sides of the neck and the loop-like course of the arteries still marking in the embryo their former position.
To a certain extent, indeed, it may be said that imperfect ossification of the vertebral column is an embryonic character; but, on the other hand, it would be extremely incorrect to suppose that the vertebral columns of the older Vertebrata are in any sense embryonic in their whole structure.
James stiffened in the approved style of erect vertebrata. "This is Madame Pierpont Pumpelly's residence," he replied with hauteur. "Madam or no madam, just slip this to her," said the shabby one. "Happy days!" Mr. Wilfred had some sort of vague idea of a law about keeping birds, but he couldn't exactly recall what it was. There was something incongruous about Mrs.
Perhaps the most startling proposition of all those which Professor Haeckel puts before us is that which he bases upon Kowalewsky's researches into the development of Amphioxus and of the Ascidioida, that the origin of the Vertebrata is to be sought in an Ascidioid form.
I have elsewhere stated at length the reasons which lead me to recognise four primary distributional provinces for the terrestrial Vertebrata in the present world, namely, first, the Novozelanian, or New-Zealand province; secondly, the Australian province, including Australia, Tasmania, and the Negrito Islands; thirdly, Austro-Columbia, or South America plus North America as far as Mexico; and fourthly, the rest of the world, or Arctogoea, in which province America north of Mexico constitutes one sub-province, Africa south of the Sahara a second, Hindostan a third, and the remainder of the Old World a fourth.
For instance, whether or not there is an open passage from the nostrils to the mouth, the only character, according to Owen, which absolutely distinguishes fishes and reptiles the inflection of the angle of the lower jaw in Marsupials the manner in which the wings of insects are folded mere colour in certain Algae mere pubescence on parts of the flower in grasses the nature of the dermal covering, as hair or feathers, in the Vertebrata.
Amongst existing Vertebrata, we find but a small amount of gradation in the structure of the eye, and from fossil species we can learn nothing on this head. In this great class we should probably have to descend far beneath the lowest known fossiliferous stratum to discover the earlier stages, by which the eye has been perfected.
It might have been expected, from some expressions met with here and there in the "Origin of Species," though not perhaps from a fair interpretation of the whole tenor of the author's reasoning, that this dearth of the highest class of vertebrata is inconsistent with the powers of mammalia to accommodate their habits and structures to new conditions.
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