THE LIVING MACHINE BUILDING FACTORS. 163 



ism. This parallelism between embryology 

 and past history has been of great service in 

 helping us toward the history of the past. At 

 one time it was believed that it was the key 

 which would unlock all doors, and for a decade 

 biologists eagerly pursued embryology with the 

 expectation that it would solve all problems in 

 connection with the history of animals. The 

 result has been somewhat disappointing. Em- 

 bryology has, it is true, been of the utmost 

 service in showing relationships of forms to each 

 other, and in thus revealing past history. But 

 while this record is a valuable one, it is a record 

 which has unfortunately been subject to such 

 modifying conditions that in many cases its 

 original meaning has been entirely obliterated 

 and it has become worthless as a historical re- 

 cord. The imperfections in regard to the record 

 were early seen after the attention of biologists 

 was seriously turned to the study of embryology, 

 but it was expected that it would be possible to 

 correct them and discover the true meaning 

 underlying the more apparent one. Indeed, in 

 many cases this has been found possible. But 

 many of the modifications are so profound as to 

 render it impossible to entangle them and dis- 

 cover the true meaning. As a result the biolo- 

 gist to-day is showing less confidence in embryo- 

 logy, and is turning his attention in different 

 directions as more promising of results in the 

 line desired. 



But although the teachings of embryology 

 have failed to realise the great hopes that were 

 placed upon them, their assistance in the formu- 



