XII] OF THE FORAMINIFERA 593 



original study of nautilus (cf. p. 518). This has accordingly been 

 done, by various writers : and in the first instance by Valerian 

 von Moller, in an elaborate study of Fusuhna — a palaeozoic genus 

 whose little shells have built up vast tracts of carboniferous 

 limestone over great part of European Russia*. 



In this genus a growing surface of protoplasm may be con- 

 ceived as wrapping round and round a small initial chamber, in 

 such a way as to produce a fusiform or ellipsoidal shell— a trans- 

 verse section of which reveals the close-wound spiral coil. The 

 following are examples of measurements of the successive whorls 

 in a couple of species of this genus. 



In both cases the successive whorls are very nearly in the 

 ratio of 1:1-5; and on this ratio the calculated values are 

 based. 



Here is another of von MoUer's series of measurements of 

 F. cylindrica, the measurements being those of opposite whorls — 

 that is to say of whorls 180° apart : 



The mean logarithmic difference is here -088, = log 1-225 ; or 

 the mean difference of alternate logs (corresponding to a vector 

 angle of 27r, i.e. to consecutive measurements along the smne 

 radius) is -176, = log 1-5, the same value as before. And this 

 ratio of 1-5 between the breadths of successive whorls corresponds 

 (as we see by our table on p. 534) to a constant angle of about 



* von Moller, V., Die spiral-gewundenen Foraminifera dea russischen Kohlen- 

 kalks, 3Iem. de VAcad. Imp. Sd., St Petershonrg (7), xxv, 1878. 



T. G. 38 



