OF FIRST CROSSES AND OF nTBRIDS. 297 



Hence it seems that, on the one hand, slight changes in 

 the conditions of hfe benefit all organic beings, and on tlie 

 other hand, that slight crosses, that is, crosses between the 

 males and females of the same species, whicli have been 

 subjected to slightly different conditions, or which have 

 slightly varied, give vigor and fertility to the offspring. 

 But, as we have seen, organic beings long habituated to 

 certain uniform conditions under a state of nature, wiien 

 subjected, as under confinement, to a considerable change 

 in their conditions, very frequently are rendered more or 

 less sterile; and we know that a cross between two forms 

 that have become widely or specifically different, produce 

 hybrids which are almost always in some degree sterile. I 

 am fully persuaded that this double parallelism is by no 

 means an accident or an illusion. He who is able to ex- 

 plain why the elephant, and a multidude of other animals, 

 are incapable of breeding when kept under only partial 

 confinement in their native country, will be able to explain 

 the primary cause of hybrids being so generally sterile. 

 He will at the same time be able to explain how it is that 

 the races of some of our domesticated animals, which have 

 often been subjected to new and not uniform conditions, 

 are quite fertile together, although they are descended from 

 distinct species, which would probably have been sterile if 

 aboriginally crossed. The above two parallel seiies of facts 

 seem to be connected together by some common but un- 

 known bond, which is essentially related to the principle 

 of life; this principle, according to Mr. Herbert Spencer, 

 being that life depends on, or consists in, the incessant 

 action and reaction of various forces, which, as throughout 

 nature, are always tending toward an equilibrium; and 

 when this tendency is slightly disturbed by any change, 

 the vital forces gain in power. 



RECiPEOCAL dimorphism: a:n"d trimorphism. 



This subject may be here briefly discussed, and will be 

 found to throw some light on hybridism. Several plants 

 belonging to distinct orders present two forms, which 

 exist in about equal numbers and which differ in no respect 

 except in their reproductive organs; one form having a 

 long pistil with short stamens, the other a short jnstil 



