232 
NATURE NOTES 
organised. Fish or vertebrate life first put in an appearance 
(as far as we know) just before the next or Devonian strata were 
deposited. In these beds, however, and in the following, or 
Carboniferous, series, they attained to a great profusion, and 
some were of gigantic size ; but they all more or less retained a 
primitive structure in having “ heterocercal ” tails, i.e., with the 
lobes unequal, a feature which the salmon only possesses during 
its infancy. Others were even simpler still, the backbones in 
almost all cases consisting of the embryonic gelatinous “ noto- 
chord.” The Carboniferous epoch saw an enormous develop- 
ment of the lower orders of plants, to which we owe our coal ; 
and at this and the following, or Permian period, the next step 
in animal life was reached, viz., the Amphibia. These amphi- 
bians, however, were all “ perenni-branchiates,” i.e., they retained 
their gills throughout their life, never reaching the stage of the 
modern frog, which loses its gills entirely and substitutes lungs. 
This higher group of Amphibia did not appear till a much later 
epoch. 
Passing on to the Secondary epoch we find the reptiles 
culminate in both size and number, many being marine, many 
others terrestrial, and others adapted for flying. One marine 
reptile only, the Amblyrhynchus of the Galapagos Islands, now 
remains to represent this lost ancestry. Certain types of terres- 
trial reptiles attained sizes even more enormous than their aquatic 
kinsfolk, and it would seem to be from some branch of this group 
that birds originated, since the earliest known bird occurs at this 
epoch and has some thoroughly reptilian features, such as teeth 
in the jaws and a long tail with the feathers arranged in two 
rows to the end of it, and not upon a “ ploughshare ” bone, as 
in modern birds. 
At this Secondary epoch, too, molluscan life assumed new 
forms. Though the genus Nautilus survives even now, the great 
family of Nautilidce had largely disappeared, and in their place 
the family Ammonitida ?, which has now entirely vanished, rose 
to its climax in numbers and variety. Fishes of one order of 
the shark family, the Cestracionida:, now represented only by the 
Port Jackson shark, were then particularly numerous, and the 
earliest representatives of the great bulk of modern fishes with 
equal-lobed tails in the adult stage, such as our salmon, herring 
and carp, appear in the early strata of this epoch. Their evolu- 
tion is attained by the stronger development of the “ hypural ” 
bones, or bones below the tip of the tail, so that, while the line 
of vertebrae is continued into the upper lobe, these hypural 
bones form the lower lobe. The first traces of Mammalia also, 
minute rat-kangaroos, occur in the Secondary period ; but no 
group other than the Marsupials has as yet been met with. 
Passing on to the last, or Tertiary epoch, we find an enormous 
influx of mammalian life to be the characteristic feature of that 
age. Here again, and perhaps more perfectly than elsewhere, 
is the great doctrine of evolution displayed, since the earlier 
