24 CHELTENHAM COLLEGE NATURAL HISTORY SOCIETY. 
group of animals the later does it appear : thus the Eozoon appears 
in the Laurentian period, Fish in the Upper Silurian, the Frog tribe 
in the Carboniferous, Birds in the middle of the Secondary, and 
Man himself not until the end of the Tertiary. 
&. If Evolution be true, all groups of animals and plants must 
have been connected by intermediate forms, i.e., there must have 
been a perfect chain from the highest to the lowest. 
To-day, of living creatures there are no two groups more distinct 
than birds and lizards—if they have always been so, the theory of 
Evolution falls! but links between the two are to be found in the 
toothed birds Hesperornis and Ichthyornis, in Archaeopteryx with its 
reptilian tail and clawed wings, and in the Deinosaurs of America 
which correspond in structure with the unhatched chick, and are 
intermediate between crocodiles and the hatched chick. 
Though there must have been a perfect series of such grada- 
tional forms between all organisms, but few of them will be found 
because of the necessary imperfection of the Geological record, and 
it is almost impossible to over-estimate this imperfection, for there 
are many animals—e.g., sea-anemones—without any skeleton or 
hard parts and such cannot become fosilised, and will therefore be 
unrepresented ; again the life of large areas will be missing ; it was 
shewn by the Challenger expedition that over thousands of square 
miles of the deep oceans there is but the slightest deposit accumu- 
lating in the sea bottom, though the surface waters teem with life: 
and lastly even though the remains should become entombed there 
are causes at work which tend to obliterate every trace of them— 
e.g., the percolation of water and Metamorphism, 
Still more rare will it be to find rocks containing a series of links 
showing the development of any given animals, for one would 
require firstly an area in which an unbroken series of strata were 
deposited for a long time, secondly, animals so numerous as to 
furnish the requsite remains, thirdly, the nature of the depesit must 
be such as to secure the preservation of the remains. Asa matter 
of fact all these conditions are best satisfied in the case of the horse, 
in which the traces of its development from a generalised mammal 
with five separate toes are forthcoming. The structure of the horse 
and every stage in its development were explained. 
The various points in the Lecture were illustrated by large 
paintings and diagrams. 
