| ↑ 1 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| Still more recently, a Pyrgoma, a member of a distinct sub-family of sessile cirripedes, has been discovered by Mr. Woodward in the upper chalk; so that we now have abundant evidence of the existence of this group of animals during the secondary period.
|
|
| → in 1859 1860 1861 1866 1869 |
| according to Agassiz, in 1872 |
|
| → difficulty on my theory, 1859 1860 1861 1866 |
| objection to these views, 1869 |
|
|
of Belgium. And, as if to make the case as striking as possible, this
cirripede was a Chthamalus, a very common, large, and ubiquitous genus, of which not one
has as yet been found even in any tertiary stratum. ↑
Hence we now positively know that sessile cirripedes existed during the secondary period; and these cirripedes might have been the progenitors of our many tertiary and existing species. |
|
| The case most frequently insisted on by palæontologists of the apparently sudden appearance of a whole group of species, is that of the teleostean fishes, low
→in
the Chalk period. This group includes the large majority of existing species. Lately, Professor Pictet has carried their existence one sub-stage further back; and some palæontologists believe that certain much older fishes, of which the affinities are as yet imperfectly known, are really teleostean. Assuming, however, that the whole of them did appear, as Agassiz
at the commencement of the chalk formation, the fact would certainly be highly remarkable; but I cannot see that it would be an insuperable
→difficulty on my theory,
unless it could likewise be shown that the species of this group appeared suddenly and simultaneously throughout the world at this same period. It is almost superfluous to remark that hardly any fossil-fish are known from south of the equator; and by running through
Palæontology it will be seen that very few species are known from several formations in Europe. Some few families of fish now have a confined range; the teleostean
might formerly have had a similarly confined range, and after having been largely developed in some one sea,
have spread widely. Nor have we any right to suppose that the seas of the world have always been so freely open from south to north as they are at present.
|
