Nov., 1890. 
ORGANIC DEATH. 
245 
sufficient period for important specific changes to have 
occurred within that period ; and in the second place, any 
noticeable change of form or size among fossil examples 
would almost certainly be referred to a distinct species. 
Precisely the same difficulties must attend the attempt to 
trace the progress of a genus. It is only in the larger groups, 
which include a wider range of difference, that a body of 
evidence can be collated sufficiently extensive to give satisfac¬ 
tory results. 
Take, for instance, the class of Fishes. It is almost 
certain that it originated with some group of soft-bodied 
animals allied to the Ampliioxus and the Lamprey, in which 
the solidification had gone only so far as to produce a cartila¬ 
ginous notochord. This was the first stage. The second is 
represented by the Sharks, Rays, and Sturgeons, in which the 
skeleton, though only cartilaginous, became fully developed, 
and the greatest increase of size was attained. The third 
stage is illustrated by the Teleostei. the comparatively small, 
but very active fish of modern times; the trout, salmon, 
herring, &c., in which the muscular power is greatly 
developed in proportion to the size. 
Take, again, the Reptilian group. Originating in some 
soft, semi-ossified amphibian, developing into the gigantic 
bony Saurians of the Lias, and then into the much smaller, 
but marvellouslv muscular, branches of the Birds on one 
hand, and the Snakes on the other. In the Birds, if not in 
the Snakes, the rise of the fourth stage, the stage of nerve 
and brain development, is shown ; and shown in connection 
with the usual phenomenon of decreased bulk, the most 
intelligent of the Bird class being undoubtedly found among 
the Insessores. 
The great class of the Mammals began with some small, 
simply organised Marsupials, expanded in the second stage 
into huge Ungulates, Proboscideans, and Carnivores, and has 
now in its third stage lost bulk but gained in muscular 
development, as evidenced in the lithe Felidae, the persistent 
hunting Canidae, and the swift Horses and Antelopes. 
The total sub-kingdom of the Vertebrata exhibits a similar 
sequence from the soft-bodied Asciaian and Ampliioxus, 
through the bony Reptiles, to the muscular Birds and 
Mammals, and finally to the intelligent Man. 
In the vegetable world the first beginnings are still 
represented by the cellular Cryptogams. The second stage 
was the epoch of gigantic Lycopods and Coniferae, in which 
the woody system predominated, with small development of 
foliage. In the third stage came the forests of broad-leaved 
Exogens with inconspicuous flowers; and the fourth stage is 
