172 STUDIES IN THE EVOLUTION OF ANIMALS 



insertion of the horns in some ancestral Rhinoceros is a question 

 difficult to answer. We have seen that in certain animals skin 

 armour has left certain marks when it disappeared, which are liable 

 to change of colour, and not impossibly the blaze on the Horse's 

 forehead may be vestigial of ancestral frontal and nose armour. 



It might lead to a certain amount of confusion to compare the 

 Horse now with a Rhinoceros, and then with a ruminant, but 

 Professor AUeyne Nicholson, in his Swiney Lectures of 1893, told 

 us that if we go back far enough in time we shall find that animals 

 which are now so distinct as ruminants and carnivora were in 

 remote times mixed up in one animal, with features that had some- 

 thing of both the branches into which that remote animal eventually 

 bifurcated. 



According to Professor Weismann's doctrine, the object of sexual 

 propagation is to mix up the separate descents of one individual 

 with the separate descents of another individual, with the view of 

 rendering the germ plasm more plastic and variable, so that it 

 may the better provide the raw material of variations in organisms 

 for the factory of adaptation by natural selection. We know that 

 the characters of two distinct species, even of two distinct genera, 

 were initially mixed up in one individual. 



Well, in bygone ages, it is very probable that animals which 

 were largely differentiated in certain anatomical features were not 

 so differentiated physiologically as to prevent their being mixed by 

 sexual mating. If this be admitted, it would follow that what we 

 now would call distinct species, might then have freely inter- 

 married,' and procreated what we now would call hybrids. For 

 instance, a mixture of hornless, one-horned, and two-homed 

 Rhinoceroses, if they happened to come together, might have inter- 

 bred and become mixed. In past ages this may have been a 

 frequent occurrence.- So with Antelopes, Horses, etc. 



