Chap. XI.] ANCIENT AND LIVING FORMS. 117 



It is no valid objection to this conclusion, that certain 

 Brachiopods have been but slightly modified from an 

 extremely remote geological epoch ; and that certain 

 land and fresh-water shells have remained nearly the 

 same, from the time when, as far as is known, they 

 first appeared. It is not an insuperable difficulty that 

 Foraminifera have not, as insisted on by Dr. Carpenter, 

 progressed in organisation since even the Laurentian 

 epoch ; for some organisms would have to remain fitted 

 for simple conditions of life, and what could be better 

 fitted for this end than these lowly organised Protozoa ? 

 Such objections as the above would be fatal to my view, 

 if it included advance in organisation as a necessary 

 contingent. They would likewise be fatal, if the above 

 Foraminifera, for instance, could be proved to have 

 first come into existence during the Laurentian epoch, 

 or the above Bracliiopods during the Cambrian forma- 

 tion ; for in this case, there would not have been time 

 sufficient for the development of these organisms up to 

 the standard which they had then reached. When 

 advanced up to any given point, there is no necessity, 

 on the theory of natural selection, for their further 

 continued progress; though they will, during each 

 successive age, have to be slightly modified, so as to 

 hold their places in relation to slight changes in their 

 conditions. The foregoing objections hinge on the 

 question whether we really know how old the world 

 is, and at what period the various forms of life first 

 appeared ; and this may well be disputed. 



The problem whether organisation on the whole has 

 advanced is in many ways excessively intricate. The 

 geological record, at aU times imperfect, does not 

 extend far enough back, to shew with unmistakeable 



