IS 77.] 
and the Evolution Hypothesis . 
523 
To elucidate the train of reasoning by which these de- 
ductions are arrived at, let us, for the sake of simplicity, 
consider the case of a hen’s egg, in which we have two 
conditions of importance ; the one consists in the protection 
of the embryo by the shell from all external influences : the 
other in the faCt that it is completely isolated from the 
mother, and therefore that its development cannot be 
affeCted by any maternal formative power. Although the 
fcetus in utero is as little influenced by modifying causes, as 
the chick in ovo, the inseCt undergoing metamorphosis in 
the pupal stage, or the seed springing from the earth, it is 
not, in the first case, on a primci facie view, so self-evident as 
in the latter ones. The conclusions we shall arrive at from 
the case of the chick will, it is evident, be nevertheless 
equally applicable by analogy to the whole of the animal and 
vegetal kingdoms. 
When quite newly laid a hen’s egg contains no trace 
whatever of the different systems, organs, and limbs which 
make their appearance in due order during the period of 
incubation, prior to which the contents of the egg are in a 
condition corresponding to protoplasm. Since the albumi- 
nous and other materials enclosed in the shell are protected 
by it from all extraneous modifying influences, the develop- 
ment of the chick (the various phases of which are precisely 
analogous both in their distinguishing traits, and in the 
order in which they occur, to those which have succeeded 
each other as characteristics of its progenitors), is undeni- 
ably effected without the aid of selection or any similar 
agent, but is due to a force within itself. Selection, there- 
fore, is not necessary to development ; but a development in 
every way analogous to that of the race is repeated in each 
individual by an agency which is not selection. The con- 
clusion seems irresistible that the race was developed by 
the same agency. The conditions in the two cases are 
similar, the effects are uniform ; are we not, therefore, 
justified in assuming that the cause in each is identical? 
It seems to follow, then , that the phenomena of ontogenesis 
and those of phylogenesis are manifestations of one and the same 
developmental law — the law of correlative expansion. 
It is worthy of notice that the earlier ancestral specific and 
generic modifications and adaptations, which undoubtedly are 
fairly attributable to natural selection, habits, See., become 
obliterated and are gradually lost, when the developing 
agent aCts free from extraneous influences, while only the 
leading types are retained. It is superfluous to have recourse 
to selection to account for racial development, when we know 
