12 EHIZOPODA. 



All these arrangements may, however, be 

 regarded as premature, pending the result of 

 further investigations into the internal structure 

 of the shell, a more extended acquaintance with 

 which must form a necessary prelude to the 

 proper classification of the Foraminifera. Since, 

 moreover, we are unacquainted with the entire 

 life-history of any one of these animals, it is 

 evident that the time has not yet arrived for pro- 

 posing such an arrangement. 



The truth of these observations ^^^ll further ap- 

 pear when we consider that in the Foraininifera, 

 more perhaps than in any other group of animal 

 forms, is the same species liable to be influenced 

 by age, by the different circumstances in which it 

 is placed, or by both of these causes combined. 

 To assign the limit to which these variations may 

 extend is, in many cases, at present impossible. 

 For it has been fully proved, in more than one 

 well ascertained instance, that two or more varieties 

 of the same species obtained from distant localities, 

 or from the same locality, but at different stages 

 of gro^vth, may present such dissimilarity of out- 

 ward aspect as to require, for the determination of 

 their specific identity, the examination of many 

 hundred individual specimens, each gradually 

 passing into the other. Hence it is easy to con- 

 ceive how, by folloAving too closely the arrange- 

 ment of D'Orbigny, different varieties of the same 

 species have been placed in separate orders ; the 

 principle on which his system has been founded, 

 namely, the direction of growth of the shell, 

 being obviously insufficient for the purposes of 

 classification. 



