SPECIES AND HYBRIDS. 99 



We shall return later to Wurtenberger's preliminary 

 communications. It was our object here to inform our 

 readers how and where modern natural inquiry sets aside 

 the phantom of species, and to enable them to judge for 

 themselves what series of observations are opposed to 

 the asseverations that in no single case has evidence 

 been given of the transition of one species into another. 

 For the old school falls into the dilemma of proclaiming 

 whole orders and classes to be *' species," and the species, 

 formerly so beautifully defined, to be varieties. 



The untenableness of the physiological part of the 

 definition of species has been conclusively shown first by 

 Darwin and afterwards by Haeckel. It is known that 

 even in a state of freedom good species not infrequently 

 breed together, and that domesticated species, such as 

 the horse and the ass, have been crossed for thousands 

 of years. But hybrids, the produce of this intercourse, 

 wxre supposed to be only exceptionally fertile, and at 

 any rate not to produce fertile progeny for more than a 

 few generations. On the other hand, it was considered 

 certain that the produce of crosses among varieties are 

 fertile in unbroken succession. The dogma of the ste- 

 rility of hybrids was formed without any experimental 

 or general observation, and by ill-luck was apparently 

 confirmed by the most ancient and best known hybridi- 

 zations of the mule and the hinny. To this familiar 

 example, in which the fertility of hybrids proves abortive, 

 we will oppose only one case of propagation successfully 

 accomplished in recent times through many generations; 

 that, namely, of hares and rabbits, two " good species " 

 never yet regarded as mere varieties. 



The numerous and varied forms of the domestic do:? 



