320 STUDIES IN THE EVOLUTION OF ANIMALS 



The evolutionary osteologist who may be still wedded to the 

 theory that every type of animal necessarily came out of another 

 type by slow and gradual modifications , accumulated by natural 

 selection, so as eventually to bring about a marked difference be- 

 tween the two, may still be hoping that future palaeontological 

 discoveries may bring to light all the intermediate links. He may 

 obtain more links than he possesses now, just as he possesses 

 graduated links between the various existing Cats and Dogs, 

 Pigeons and Fowls. 



But even if the whole of the geological formations of the earth 

 were explored, I should not anticipate that he would find all the 

 links he may hope for. Teratology plainly indicates that * leaps,' 

 without much trace of graduated intermediate links, can occur now, 

 and therefore most probably similar leaps were not uncommon in 

 the days when the physical conditions of life must have been far 

 less equable than we now know them. 



It would be curious if the study of abnormalities should give 

 us an insight into the origin of what we call normalities, 



Mr. J. A. Thomson * writes : * Among back-boned animals we 

 recall the teeth of the Shark, and the sword of the Sword-Fish, the 

 venomous fangs of Serpents, the jaws of Crocodiles, the beaks and 

 talons of Birds, the horns and hoofs of Mammals. Now we do not 

 say that these and a hundred other weapons were from their first 

 appearance weapons, indeed we know that most of them were not. 

 . . . By sheer use a structure not originally a weapon became 

 strong to slay.' 



Just so ; and the sudden appearance of a monstrous part would 

 produce one of two results : 



(a) Either it would have no appliances of muscles and nerves 

 to utilise it in the struggle for existence, and then it would be 



1 Study of Animal Life, p. 34. 



