THE FORAMINIFERA 



61 



young individuals of this form did not come under Munier- 

 Chalmas's observation. He was thus at first inclined to the view 

 that the individuals of the two sets, although in some way dis- 

 tinct in nature, began life under one form, namely, that with a 

 large central chamber. At a certain stage, it was supposed, the 

 growth of one set of individuals was arrested, while in the 

 members of the other set the walls of the large central chambers 

 were absorbed, and growth was continued not only by the addition 

 of chambers at the periphery in continuation of the series of those 

 already formed, but also in a centripetal spiral towards the centre 



FIG. (5. 



Nummulites laevigata, Lam. A, Central portion of a section of the megalospheric form 

 (" N. lamarcki," d'A.) ; B, of the microspheric form. Both x 10. (After de la Harpe, 17.) 



of the shell, filling the space originally occupied by the large 

 central chamber. 



This idea of the relationship of the two forms was controverted 

 by de la Harpe, who pointed out, expressing his own views and 

 those of de Hantken, that young examples of the form with a 

 small central chamber are known to occur, and also that differ- 

 ences may be detected not only at the central parts of the shells 

 of the two forms of nummulites, but throughout the series of 

 chambers. Thus it is often found to be the case that in the forms 

 with a large central chamber (A, Fig. 6) the maximum size of the 

 chambers subsequently added is attained early in the series of 

 whorls, while in the others (B) the size of the chambers gradually 

 increases to the last whorl. 



While the view that one form results from the modification of 

 the other was thus shown to be untenable, it was suggested that 



