THE WONDER OF LIFE 615 



cartilage — a tell-tale cartilage. In white races it is a great 

 rarity, occurring in less than one per cent. Giacomini 

 found it in four cases out of five hundred and forty-eight 

 whites. But he found it twelve times in sixteen coloured 

 people, and Adachi found it five times in twenty-five 

 Japanese. More recently Dr. Paul Bartels examined twenty- 

 five South African natives (eight Hereros and seventeen 

 Hottentots) and found the teU-tale cartilage in twelve. 

 The cartilage is found in all Apes and Monkeys, and although 

 no living Ape or Monkey is ancestral to Man, the cartilage 

 is a Simian feature, persisting in Man since the remote 

 period when the human stock diverged from the Simian. 

 The facts show that some races are in this instance as in 

 others, more theromorphjc than others — ^more conser- 

 vative of their historical reUcs. 



One has, of course, to be careful in using this interpre- 

 tation of peculiarities as atavisms. It is probable that in 

 some cases all that we are justified in saying is that a varia- 

 tion occurs which happens to be along very antique lines. 

 To take an example, the teeth of mammals begin as in- 

 growths of the (ectodermic) epitheUum into the (meso- 

 dermic) connective tissue of the gum, whereas the teeth 

 of sharks and skates and other Selachian fishes begin as 

 papillae of the mesoderm which grow up into the epidermis. 

 The teeth of Selachians are just transformed scales, turned 

 to a new use. But it is a remarkable fact that the Sela- 

 chian or placoid mode of tooth development does occur 

 in Bony Fishes, tailed Amphibians, and in the crocodile. 

 Rose has seen hints of it in the human embryo, and not 

 long ago (1911) Adloff found in a human embryo, of about 

 nine weeks, a freely projecting epithelial papilla Ijdng 

 beside a normal tooth-germ. He regarded it as an atavistic 



