The Use of Graphs in Paleontology. 405 
series ; but that + is very much out of accord with all the others, 
and therefore lies quite distinctly off the true line of descent. 
GENERAL REMARKS. 
In laying emphasis upon the principal of the independence of 
flow-lines of change in structural elements it is not intended to deny 
the principle of the correlation of parts. On the contrary, it is held 
that the wonderful correlation of parts, which characteriz2 all 
organisms which survive the vicissitudes of ever - changing 
surroundings, is the outcome of a continual adjustment of the parts 
to one another. Such an adjustment can be attained only if the 
parts are free to change this way or that with independent velocities. 
Only by such independence, for example, could the five-toed primitive 
mammals have given rise to such diverse types of feet as those of the 
horse, the elephant, and the sloth. 
100 
90 
50 
E 
Fic. 10.—Series of graphs representing the mutations of the gens 
Caninia cylindrica. 
Whilst a description of these three types of feet may be quite 
diagnostic of these three mammals, it is not diagnostic of the genetic 
series to which each belongs, for such a series exhibits continual 
change as it is followed through time. In this case, it is the direction 
and velocity of change in homologous parts which is diagnostic. 
In paleontology the time factor is of supreme importance. On this 
account it is not the species, but the flow-lines of change, with or 
without clearly defined structural units, which provide the easiest 
points of attack for the study of evolutionary problems. Indeed, 
the separation, and the elucidation of the behaviour of these flow- 
lines, which clustered together constitute the lineages of various 
groups, is a necessary preliminary to the unravelling of phylogenies 
and the solving of problems in heredity. 
As already shown, homologous units in separate genetic series 
