SPECIES AND IIYBRIDS. 99 
We shall return later to Wiirtenberger’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, 
were 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 dog 
