28 ORGANIC DEPENDENCE AND DISEASE 



study; it is too soon to determine its value and to discuss 

 it here is inappropriate, but we must at least grant to these 

 suggestions the probability that we have heretofore greatly 

 underestimated the time required for the upbuilding of the 

 fossiliferous rocks and for the evolution of life. In terms 

 of millions of years time becomes incomprehensible and the 

 sum total, whatever it may be, must be regarded as com- 

 petent for all the evolutionary processes of life and work. 



INDEPENDENCE OF THE FIRST FAUNA 



We still stand in ignorance of the real primitive or in- 

 ceptive fauna of the earth, and when we use the expression 

 "first fauna," it is with the reservation which absence of 

 facts compels. We may speak freely, however, of the first 

 fauna known to us and with a fulness of knowledge that 

 justifies, in good measure, deductions regarding the nature 

 of its ancestors upon earth. The fauna of the Cambrian 

 system represents to us the actually known first fauna, for 

 evidences of organic life in the rocks before and below 

 the Cambrian are desultory though positive. While we are 

 considering the special nature of the Cambrian fauna from 

 the point of view we have here taken, let it be not forgotten 

 that this so-called "first fauna" must have been millions 

 of years in the making, worked out by the slow and arduous 

 advances with which first steps have ever been taken in the 

 course of nature. Our ' ' first fauna, ' ' then, is also the prod- 

 uct of the ages ; and in spite of its complexion of simplicity, 

 the entire absence in it of the vertebrate type and of what 

 we are wont to regard the more progressed of its inverte- 

 brate types, specialization in anatomical structure is per- 

 haps, in view of our expectations, the most obvious fact that 

 it sets forth. Let us keep this important fact in mind as we 

 study its composition with reference to independent and de- 

 pendent life. 



