3^ Evolution by Expansion. [January, 
can be behind another in its stage of development. Thus 
the dog-fish, skate, and other fishes of the kind have par- 
tially lost most of their fish-charaCteristics together. The 
bristles of the dog-fish and other cartilaginous fishes may be 
regarded as rudimentary fur, such as the seal possesses. 
Most apes have simultaneously lost the callosities, the 
cheek-pouches, the tail, the pointed ears, &c., peculiar to 
the monkey proper. The swinging of a man’s arms in 
unison with the movements of his legs in walking has 
reference to correlative development. 
Darwin regards rudimentary parts that are apparently 
disappearing as in a state of decadence through disuse ; 
he fails, however, satisfactorily to explain the existence of 
those in a nascent state, but of no present use ; still 
less of those in an apparently permanent condition — such 
as the mammae of males. It is difficult to imagine that the 
sexes of Mammalia were ever so confused as to give rise to 
this phenomenon, especially when the sexes of their imme- 
diate progenitors are so perfectly defined. 
There is another difficulty, with regard to organs in this 
state, that Darwin freely confesses has fairly baffled 
him ; natural selection alone cannot account for it. He 
admits that some additional explanation, which he cannot 
give, is necessary to explain the still further reduction in 
size or complete obliteration of an organ that appears to 
have reached the limit of decadence from disuse, and that it 
is scarcely possible that disuse can go on producing any 
further effeCt after the organ has once been rendered func- 
tionless. The explanation of this case, as well as of all 
other cases of rudimentary growths, is obvious enough on 
the theory of correlative expansion. Thus it would appear 
that all parts of an organism and its characteristic features 
are functions of one another and of the whole organism, and 
all vary together. The symmetry of form, so noticeable 
throughout animate nature, is another result of the laws of 
correlation. Were natural selection permitted to mould the 
forms of life around us, uncontrolled and undirected by a 
supreme force, that of correlative expansion, shapes the 
most grotesque and monstrous would inevitably inhabit the 
globe. 
Instances showing that type is independent of the con- 
ditions of existence, that rudimentary parts can be satisfac- 
torily accounted for only by regarding their existence as due 
to correlation of growth or expansion, and that correlative 
expansion is a phase of the phenomenon of conformity to type, 
might be multiplied to any extent. 
