140 REVIEWS. 



former times they were as liable to variation as they now are ; 

 ami if the individuals of the same species may claim a common 

 local origin, — then we cannot wonder that " the theory of 

 a succession of forms by deviations of anterior forms " should 

 be regarded as " the most natural hypothesis," nor at the 

 general advance made towards its acceptance in some form or 

 other. 



The question being, not, how plants and animals originated, 

 but, how came the existing animals and plants to be just 

 where they are and what they are ; it is plain that naturalists 

 interested in such inquiries are mostly looking for the answer 

 in one direction. The general drift of opinion, or at least of 

 expectation, is exemplified by this essay of De Candolle ; and 

 the set and force of the current are seen by noticing how it 

 carries along naturalists of widely different views and prepos- 

 sessions, — some faster and farther than others, — but all in 

 one way. The tendency is, we may say, to extend the law of 

 continuity, or something analogous to it, from inorganic to 

 organic nature, and in the latter to connect the present with 

 the past in some sort of material connection. The generali- 

 zation may indeed be expressed so as not to assert that the 

 connection is genetic, as in Mr. Wallace's formula : " Every 

 species has come into existence coincident both in time and 

 space with preexisting closely allied species." Edward Forbes, 

 who may be called the originator of this whole line of inquiry, 

 long ago expressed a similar view. But the only material 

 sequence we know, or can clearly conceive, in plants and 

 animals, is that from parent to progeny ; and, as De Candolle 

 implies, the origin of species and that of races can hardly be 

 much unlike, nor governed by other than the same laws, 

 whatever these may be. 



The progress of opinion upon this subject in one generation 

 is not badly represented by that of De Candolle himself, who 

 is by no means prone to adopt new views without much con- 

 sideration. In an elementary treatise published in the year 

 1835, he adopted, and, if we rightly remember, vigorously 

 maintained, Schouw's idea of the double or multiple origin of 

 species, at least of some species, — a view which has been 



