THE LIVING MACHINE BUILDING FACTORS. 141 



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. Embry- 

 ology 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 mean- 

 ing has been entirely obliterated and it has become 

 worthless as a historical record. These imper- 

 fections in regard to the record were early seen 

 after the attention of biologists was seriously 

 turned to the study of embryology, but it was ex- 

 pected 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 modi- 

 fications are so profound as to render it impos- 

 sible to untangle them and discover the true 

 meaning. As a result the biologist to-day is show- 

 ing less confidence in embryology, and is turning 

 his attention in different directions as more promis- 

 ing of results in the line desired. 



But although the teachings of embryology 

 have failed to realize the great hopes that were 

 placed upon them, their assistance in the formula- 

 tion of this history of the machine has been of 

 extreme value. Many a bit of obscurity has been 

 cleared up when the embryology of puzzling ani- 

 mals has been studied. Many a relationship has 



