52 
thesis Are all the phenomena observable in Nature, which 
Sid bt if Darwinism be true ? The extent and preten- 
sion of the hypothesis expose it to the severest possible tests 
in this respect! If all living beings have indeed descended 
from a very few original progenitors, then there mjt flow 
from this certain well-marked characteristic m respect (1) to 
their present nature and relations (2) to their 
space and (3) to their distribution m time. Undei tnese 
Xee heads, then, I propose to consider the most important 
of the tests of consistency to which Darwinism is fairly 
subject, confining myself as before to a general outline, wit - 
° U Fhst 1 then M o 1 f tht° present characteristics of living beings^ 
their nature and relations to one another. The principle of 
Darwinism being the development of a vast number of 
forms by gradual divergence from a single original, it follows 
atTnce that if the hypothesis be true, all such forms should 
be capable of being arranged in groups o f 
diversity, retaining, however, even to the last, some chaiac 
teristics in common. Not only should we , 0 le 
every species resemblances to the first progenitor of whole, 
but U resemblances to the various intermediate membe^ of 
the series, these resemblances increasing as the line approached 
its termination ; the whole sum of characteristics possessed by 
each species being the result of successive ad^ 0113 "^ 011 ^ 
common characteristics belonging to the wt • 
precisely so we find it. The whole natural system of classi 
ficationm based upon this principle of group within group , 
first species, then genera, then sub-orders, orders, sub -classe.,, 
classes ■ the amount in common constantly diminishing a 
ascend ’ yet something, and often a good deal, in common 
being found even to the last. This latter is an important 
point Look for example at two of the great classes of pla , 
exogens and endogens^-what a group of charaeteris i^ does 
each present. Here are the exogens, growing by the forma- 
tion of additional layers outside the old 
cotyledons in their seed, having leaves with rebooted veins 
and flowers with the parts most commonly m staples < of fou 
or five. Here are the endogens, growing by addition to the 
inside, possessed of but one cotyledon,, having leaves with 
parallel veins, and flowers with the part* 
And these characteristics are common to all the myriads 
cnrders, genera, and species which each class contains All 
exactly as was to be expected if the Darwinian hypothesis 
W TWurther, it is to be noted that the distinction between 
