216 REVIEWS. 



should better apprehend the persistence of species, and feel 

 the great improbability that the stream will ever escape from 

 its ancient and well-worn bed, and strike into new courses. 



Now, in the first place, the more lively the conception we 

 thus form of the invariability of species, through a happy 

 metaphorical illustration of it, the more unlikely does it appear 

 that early characters, long lost in the flow, should reappear 

 through atavism as varieties. To continue the simile, the more 

 impetuous the stream, the less the possibility of its turning 

 back upon itself, and resuming old characteristics. The eddies 

 of atavism (the resumption of dropped characters) are not 

 likely to extend back very far ; and it seems gratuitous to 

 have recourse to them in explanation of new forms. More- 

 over, although the stream has made its bed and lies in it, not 

 escaping from its own valley, it is flexible enough to obstacles, 

 is ever changing its particular course as it flows, and may by 

 its own action send off here and there a bayou (variety) or 

 branch into a delta of channels (derivative species). 



Like Agassiz, Naudin conceives of species as originating 

 with a large number of individuals of the same structure, and 

 of which numerous reciprocal crosses have determined the 

 direction of the line in which their posterity have evolved. 

 But he maintains that these individuals, and all existing spe- 

 cies, had a common origin in a " proto-organism " ; and that 

 the various lines of descent acquired fixity into species only 

 as they acquired sexuality. If we rightly apprehend it, Nau- 

 din's idea of the purport of sexual reproduction (as contrasted 

 with that by buds) is to give fixity to species. Our idea is 

 a different one, both as to the essential meaning of sexuality 

 and as to its operation in respect to fixity. His conception 

 may be tested by inquiring which are the more variable, or 

 sportive, seedlings or plants propagated from buds. This we 

 suppose can be answered only one way. 



M. Naudin is a veteran and excellent investigator, and 

 nothing which he writes is to be slighted. We have frankly 

 set down our impressions upon a first perusal of bis important 

 communication ; but are ready to revise them, if need be, upon 

 more deliberate consideration. 



