XII] 



OF THE FORAMINIFERA 



597 



may see by Fig. 313 ; where the angle subtended by each chamber 

 is made equal to 20°, and this diagrammatic figure is not per- 

 ceptibly different from the other. In some cases the subtended 

 angle is less constant ; and in these it would be necessary to equate 

 the several linear dimensions with the corresponding vector angles, 

 according to our equation r = e^^ota j^ ^^ probable that, by so 

 taking account of variations of d, such variations of r as (according 

 to Rhumbler's measurements) Pulvinulina and other genera 

 appear to shew, would be found to diminish or even to disappear. 



Fig. 313. Cyclammina sp. (Diaurammatic.) 



The law of increase by which each chamber bears a constant 

 ratio of magnitude to the next may be looked upon as a simple 

 consequence of the structural uniformity or homogeneity of the 

 organism ; we have merely to suppose (as this uniformity would 

 naturally lead us to do) that the rate of increase is at each instant 

 proportional to the whole existing mass. For if Vq, F^, etc., be 

 the volumes of the successive chambers, let Fj bear a constant 

 proportion to Vq, so that V-^ = qVQ, and let V^ bear the same 

 proportion to the whole pre-existing volume : then 



^2 = q (Fo +V,)^q (Fo + qV,) ^ qV, (1 + q) and V^jV^ = l + q. 



