THE HORSE OF THE PRESENT AND THE PAST 481 



series of phenomena would be exhibited! Instead of sitting on lier eggs 

 for weeks, the common hen would find her brood at the expiration of a 

 few days hatched but palpably unfinished, very unlike the chickens to 

 which she had been accustomed. The young living beings would present 

 some of the characteristics of the mammal, but they would also, in certain 

 parts of their organism, show structures connecting them with reptiles, and, 

 in the arrangement of the blood-vessels, they would run the risk of being 

 classed among fishes. 



Day by day almost imperceptible changes would i)e distinguished by 

 the critical observ^er, and gradually the unnamed living thing would assert 

 its claim to be accepted as a bird, and finally the expert would decide, 

 without the least chance of making a blunder, to which particular species, 

 genus, and variety of birds the mysterious creature belonged. In like 

 manner it might be supposed, for the sake of illustration, that the mare, 

 instead of producing a foal at the end of several months, would give birth 

 at an earlier period to an unfinished organism in which some of the charac- 

 teristics of the lower Vertebrata would be recognized, those of the reptile or 

 the fish, for example. Gradually advancing day by day, the young organ- 

 ism would exhibit in turn, in the circulatory system especially, some of 

 the features belonging to the bird, and passing through the changes which 

 mark certain phases in the organization of the lower mammals, it would 

 arrive at the stage of perfect development and assume the form of the parent. 



In reply to the very easy and obvious criticism that the above 

 descrijDtion is absurd, and that the processes referred to could not possibly 

 take place, it may be observed that nothing has been advanced of a hypo- 

 thetical character. All the changes or metamorphoses referred to do 

 constantly occur, and the only liberty which has been taken has been 

 that of supposing them to be visible. Facts which are invisible to the 

 ordinary observer, but perfectly distinct to the skilled microscopist, have 

 been assumed to occur in such a position that they might be recognized by 

 the unaided eye. The facts are not the less real because they do not 

 present themselves in a palpable form. In the study of embryology all 

 these changes are recognized, but they are visible only by the aid of the 

 microscope. If they formed part of the ordinary observation of the breeder 

 of stock, as they do of the investigations of the scientist, the mysterious 

 doctrine of evolution would lose its glamour, and become one phase of mere 

 commonplace experience. 



Replying to some of the objections which have been urged against the 

 docti'ine of evolution, the late Herbert Spencer deals with two forms of 

 criticism which have often been advanced, one relating to the ol^vious and 

 admitted fact that the process of evolving a new species has never been 



