414 



THE FORMS OF CELLS 



[CH. 



parts of the ramified mass. When we look more closely at the 

 arenaceous forms, we find the same thing true of them; they 

 represent, in whole or part, approximations to the surfaces of 

 equilibrium, spheres, cylinders and so forth. In Aschemonella we 

 have a precise rephca of the calcareous Ramuliyia; and in Astrorhiza 

 itself, in the forms distinguished by jiaturalists as A. crassatina, 

 what is described as the " subsegmented interior*" seems to shew 



Fig. 130. Various species of Zagrew«. After Brady. 



the natural, physical tendency of the long semifluid cylinder of 

 protoplasm to contract at its limit of stability into unduloid 

 constrictions, as a step towards the breaking up into separate 

 spheres : the completion of which process is restrained or prevented 

 by contact with the unyielding arenaceous covering. 



Passing to the typical calcareous Foraminifera, we have the most 

 symmetrical of all possible types in the perfect sphere of Orbulina ; 

 this is a pelagic organism, whose floating habitat gives it a field of 



♦ Brady, Challenger Monograph, pi. xx, p. 233. 



