128 MODERN IDEAS OF EVOLUTION 



distinct in its properties from that which develops 

 into another kind of animal, even though no obvious 

 difference appears to us, we have no ground for sup 

 posing that the early stages of all animals are alike ; 

 and when we rigorously compare the development of 

 any animal whatever with the successive appearance 

 of animals of the same or similar groups in geological 

 time, we find many things which do not correspond, 

 not merely in the want of links which we might 

 expect to find, but in the more significant appearance, 

 prematurely or inopportunely, of forms which we 

 would not anticipate. Yet the main argument of 

 Haeckel s book is the quiet assumption that anything 

 found to occur in ontogenetic development must also 

 have occurred in phylogenesis, while manifest diffi 

 culties are got rid of by assuming atavisms and 

 abnormalities. 



A third characteristic of the method of the book 

 is the use of certain terms in peculiar senses, and as 

 implying certain causes which are taken for granted, 

 though their efficacy and mode of operation are 

 unknown. The chief of the terms so employed are 

 heredity and adaptation. Heredity is usually 

 understood as expressing the power of permanent 

 transmission of characters from parents to offspring, 

 and in this aspect it expresses the constancy of 

 specific forms. But as used by Haeckel it means the 

 transmission by a parent of any exceptional cha 

 racters which the individual may have accidentally 



