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“ When astronomers found the calculable influence of the law 
of gravitation on the motion of the planets disturbed, and pro tanto 
counteracted by some unexplained and undiscovered agency, they at 
once confidently inferred the existence of an unknown body at an 
unguessed distance, but in a specified direction. They believed in 
Neptune long before they found him. Why should we not do in 
physiology what they did in physics ? ”—(W. R. Greg. Enigmas of 
Life. p. 6g.) 
Mr. Wallace speaks to the same effect. 
“ When the geologist explains how the contour of a country has 
been formed by rain and ice, it is not said that he has explained 
nothing, unless he goes on to show exactly how rain and snow are 
formed, or even goes further back to the cause of gravitation, which 
is really what gives them all their power to do any work ; and when 
the physicist explains how thunder and lightning are produced by a 
reference to the electric spark and its accompanying sound, he is not 
told that the explanation is valueless till he has discovered the nature 
and cause of electricity itself.”—(Wallace. Nineteeiith Century, 
vol. vii., p. ioj.) 
Mr. Darwin asserts that certain variations could not have 
been caused by the direct action of the conditions of life. 
Let us take one of the cases he cites, viz., the modified 
skull of the Niata ox. 
“ This breed bears the same relation to other breeds, as bull or pug 
dogs do to other dogs ; or as improved pigs do to common pigs. The 
common codfish presents a similar monstrosity, called by the fisher 
man the bulldog cod. Almost a similar conformation characterises 
the extinct and gigantic Sivatherium of India.”—(The Variation, 
vol. i., pp. 8g-gi.) 
It may be well to compare the assertion of Mr. Darwin, 
that the Niata cattle could not have been caused by the 
direct action of the conditions of life, with what he says of 
the domesticated pig, which resembles the Niata cattle in 
the characteristic formation of its skull. 
He quotes, apparently with approval, the argument of 
Nathusius, that the shape of the skull is largely due to 
plentiful food in an early period of life, and to a change of