THE BEGINNINGS OF LIFE. 611 



a short time in action, the modification generated will 

 be evanescent; for concluding that a modifying cause, 

 acting even for many generations, will do little towards 

 permanently altering the organic equilibrium of a race ; 

 and for concluding that, on the cessation of such cause, 

 its effects will become unapparent in the course of a few 

 generations.' 



The question, therefore, as to the mode of explana- 

 tion of the existence of very simple organisms at the 

 present day, merges in an almost insensible manner 

 into that concerning the explanation of the existence of 

 so-called Persistent Types. 



The Foraminifera, for instance, are organisms which, 

 from the absence of all sexual distinctions, and from 

 the extreme simplicity of their body-substance, ought, 

 in spite of the notable complexity of the shell-like 

 structures which many of them inhabit, undoubtedly 

 to rank amongst the ephemeromorphs. The ani- 

 mal substance of these organisms differs little from 

 that of Amoebae, Arcellirce, and other simple Rhizo- 

 pods; and, moreover, we are distinctly informed by 

 Dr. Carpenter that any such definite assemblages of 

 individuals as are usually included under the word 

 c species ' do not exist amongst them. He says : 

 c The range of variation is so great amongst Forami- 

 mfera. as to include, not merely the differential charac- 

 ters which systematists, proceeding upon the ordinary 

 methods, have accounted specific, but also those upon 

 which the greater part of the genera of this group have 

 R r 2 



