THE LIVING MACHINE BUILDING FACTORS. 161 



been left samples of many of the steps in this his- 

 tory of machine building. The history can be 

 traced by the study of these samples just as the 

 history of any machine might be traced from a 

 study of the models in a patent office. One might 

 very easily trace, with most strict accuracy and 

 minute detail, the history of the printing machine 

 from the models which are preserved in the 

 patent offices and elsewhere. So is it with the 

 history of the living machine. To be sure, the 

 history is rather incomplete and at times difficult 

 to read. Many a period in the development has 

 left no samples for our inspection and must be 

 interpreted in our history between what went 

 before and what comes after. Many of the 

 machines, especially the early ones, were made 

 of such fragile material that they could not be 

 preserved in the rocks. In many a case, too, the 

 rocks in which the specimens were deposited 

 have been subjected to such a variety of heatings 

 and pressures, that they have been twisted out 

 of shape and even crushed out of recognizable 

 form. But in spite of this the record is showing 

 itself more complete each year. Our palaeonto- 

 logists are opening layer after layer of these rocks, 

 and thus examining each year new pages in 

 nature's history. The more recent epochs in the 

 history have been already read with almost 

 historic accuracy. From them we have learned 

 in great detail how the finishing touches were 

 given to these machines, and are able to trace 

 with accuracy how the somewhat more general- 

 ized forms of earlier days were changed to pro- 

 duce our modern animals. 



