80 LIFE AND OEGANISATION. 



generality ; and the possibility might be urged of numerous 

 such instances, if time and chances are taken into account. 

 But we doubt much whether, in the animal kingdom at least, 

 an unequivocal case of this kind really exists. It may be 

 admitted that several hybrid species (the equine, canine, 

 ovine, and, possibly, but less certainly, some other animals 

 brought immediately under human culture) are to a certain 

 extent prolific.* But the true hybrid does not propagate 

 with the hybrid; and its power of propagation, even with 

 the perfect species, is very limited in degree, and soon comes 

 to an end. On the other hand, we believe there to be no 

 recognised instance of absolute infertility in two varieties of 

 the same stock, however wide their deviation from each 

 other. This argument, then, for transmutation halts on the 

 very threshold; and, duly examined, may even be appro- 

 priated for the opposite conclusion. 



The sexual relations cannot be omitted as a point in this 

 question. Weighing fairly all the circumstances and, 

 amongst others, the period of gestation (different even in 

 the cognate species of the dog and wolf, though alike in the 

 dog and jackal) it appears almost certain that no real or 

 permanent change of species can take place without a con- 

 current mutual adaptation of the two sexes in its progress ; 

 a contingency so improbable, seeing all that is required, 

 that we cannot but regard this as one of the most cogent 

 objections to the doctrine before us, and meriting more 

 attention than it has usually received. 



A word or two more must be said in regard to the varieties 

 in species themselves. Strictly speaking, these are not so much 

 structural differences, as variations in size, configuration, 



* We are bound to notice here the experiments of M. Kouy of Angouleme, 

 who succeeded, by the inter-breeding of hares and rabbits, in producing a new 

 hybrid race, fertile, as he alleges, without reversion to the original stock. 

 Further research is required to attest the duration of this fertility. 



