4. THE DARWINIAN HYPOTHESIS I 
distinct species than when fertilised by its proper 
pollen! On the other hand, the famous Gaertner, 
though he took the greatest pains to cross the 
Primrose and the Cowslip, succeeded only once or 
twice in several years;. and yet it is a well- 
established fact that the Primrose and the Cow- 
slip are only varieties of the same kind of plant. 
Again, such cases as the following are well estab- 
lished. The female of species A, if crossed with 
the male of species B, is fertile ; but, if the female 
of B is crossed with the male of A, she remains 
barren. Facts of this kind destroy the value of 
the supposed criterion. 
If, weary of the endless difficulties involved in 
the determination of species, the investigator, 
contenting himself with the rough practical 
distinction of separable kinds, endeavours to 
study them as they occur in nature—to ascertain 
their relations to the conditions which surround 
them, their mutual harmonies and discordancies of 
structure, the bond of union of their present and ~ 
their past history, he finds himself, according to 
the received notions, in a mighty maze, and with, 
at most, the dimmest adumbration of a plan. 
If he starts with any one clear conviction, it is 
that every part of a living creature is cunningly 
adapted to some special use in its life. Has not 
his Paley told him that that seemingly useless 
organ, the spleen, is beautifully adjusted as so 
much packing between the other organs? And 
