IO2 EVOLUTION OF TO-DAY. 



gelatinous rod for a back-bone, and this could not 

 have been preserved as a fossil. If this animal pos- 

 sessed scales, the scales might have been preserved ; 

 and we do find certain fish-scales at this period. 

 But simple scales of course give us no idea as to 

 what sort of an animal possessed them. For all that 

 we know this animal may have been exactly the syn- 

 thetic type we are looking for. And so in many 

 cases, the early ancestral forms of various groups 

 must have been animals with very few hard parts, 

 and there would be, therefore, no chance of their 

 preservation. 



A second reason for the abundance of specialized 

 forms compared with the synthetic types is, that 

 they doubtless existed in greater numbers. Nor is 

 this begging the question, as it at first sight seems to 

 do. A synthetic type can only remain synthetic by 

 existing in small numbers. All experience teaches 

 us that as soon as any animal begins to multiply 

 rapidly it becomes rapidly specialized. It is only 

 specialized forms which can exist in great num- 

 bers. As a result, we should expect to find, at all 

 ages, that those forms which become specialized to 

 adapt themselves to peculiar conditions, would mul- 

 tiply the most rapidly and exist in the greatest num- 

 bers. Here, then, is a reason for the comparative 

 scarcity of forms with generalized characteristics, at 

 all geological ages, a reason which would be as sig- 

 nificant in early times as at present. A synthetic 

 type can remain synthetic only as long as it exists 

 in small numbers. 



